(this topic has been edited a bit to make it more to the point. It's also been edited to reflect on some ideas of others in this thread)
TL;DR: HEY THE MAIN GAME STORYLINE CAN BE CONFUSING MAYBE WE SHOULD FIX THATI'll start off with an anecdote from when I started playing, which is on-topic with some thoughts on the game's storytelling and timeline, and how confusing it can be for new players (especially questers) to play ESO.
I joined the game back in early 2016. I played through all of AD and Coldharbour, and a little over two weeks later, I finished the main quest finale. To say I was hooked would be an understatement. I immediately fell in love with the game.
Next up was Cadwell's Silver, which took me to EP. At this point I was starting to see a pattern. Five zones for each alliance, each one with their own little story. And they all followed a main story. I played through Bleakrock Isle, then Bal Foyen, and then Stonefalls.
But in Stonefalls something happened. I played the story quests up until Fort Virak, and when I finished there, I couldn't find a quest leading me to the next place. Where did the road lead? Up to Skyrim, and me, having no clue where I was supposed to head went stumbling into The Rift.
But when I spotted the first enemy NPC, its CP had shot up! I could kill him, yes, but he was significantly harder to deal with. I wasn't sure if that was intended, so I decided to press on. I went on to Fullhelm Fort, where there was a quest! Finally, something to get into to get a sense of this zone's questline. But yet again, something was very... off. The quest giver, Sergeant Sjarakki, had some of the most spoiler-y and confusing dialogue I had seen so far. It didn't make sense, so I just tuned out for it, and decided to write it off as a particularly badly written quest. Surely it's fine, right? I move on with my exploration, to Forelhost. There I find another quest, which seems linked to the one before. The quest is a little less nonsensical, there's a brave Dunmer woman there soldiering through. I help her warm up, explore the ruin, kill a dragon priest. That was fun.
So two quests in that didn't make sense, I head down the road to Trollhetta. There's a Pact camp, here, and Jorunn the Skald-King is the quest-giver. And yet, he is oddly informal, for an enemy king. One might even think he knows the player well! Why? No idea, and there's no questions I can ask. The Worm Cult is here, and we need to act. I accept the quest, carve my way through the enemy forces, cutting down undead giants and cultists along the way, until I reach the final boss... a ghost giant named Sinmur!
But who IS he?!
I begin to realize that I've done something wrong. somehow. Did I miss a quest somewhere? Did I miss a book that explained? I think on that while I battle the ghost giant. And then, when I kill him with what I at the time thought was some great help from the NPCs, I am hit with this:

I have just played the final quest of EP with no context. Yay! I get kinda depressed having no idea where the zone's storyline started, so I push on exploring both The Rift and Eastmarch in the reverse order. Then after Windhelm I go back to Fort Virak, and there I'm able to pick up a quest I missed, which leads to Kragenmoor. From there I play all the way to Shadowfen until I get boated to Eastmarch again. To then explore the quests in the chronological order, I had to make an EP character specifically to do that. When I was able to play the story quests from start to finish I started to understand the questline a lot better, and it made a lot more sense.
REGARDING NEW QUESTERS:
TESO can be very hard to get into for questers, when it comes to its base-game's storytelling. Ever since the game went open-world, it's become very similar to the rest of the TES singleplayer games, which was a breath of fresh air. However the legacy of ESO is a railroad MMORPG. While I agree that to railroad players can be bad, I also think that it makes the storyline a cohesive whole. The storyline, whether it's written poorly or well, is a linear chain of events. Which is why we now have a problem. When One Tamriel came out, players could play through the main quest storyline without having to level up. While this meant you had to wait to finish it and level your soul magic, you were also encouraged to explore your alliance's zones and story, which logically made your character famous or renowned.
With the original tutorial you'd get an account from The Prophet, then, almost immediately next to you there was a quest giver offering an account of how you fell into the sea and got fished up, which leads you into your alliance quest line.
However these days, you can do the Coldharbour starting quest, run between a cave and city a couple of times, helping a small band of people gather together, and all of a sudden, you get contacted by Vanus Galerion himself, who says you're the best candidate to negotiate with the alliance leaders,
even though you have done NOTHING NOTEWORTHY that anyone has heard of. You, a nobody, is the hero that the world needs. Nobody has heard of you, nobody has met you, nobody can speak in support of you. You, a literal cave-dweller, is the most suited candidate to save the world, because.... uh, idk. Reasons.
With the release of the chapters and their unique tutorials, the main story has become increasingly obscure. I don't think it matters that a priest shows up and tells you to meet a benefactor when you port into one of the base game zones, because the main story has had its link to the alliance storylines completely removed. Several quests in the base game not required for the story can only be completed because the Vestige (the player character) has no soul, with literal dialogue quotes going something like "Not a problem, I don't have a soul!"
The official TESO Reddit page is constantly having threads written from players that don't know how to make sense of the story of the base game. I have spoken to countless new players who have told me about their frustrations with the storyline. I've given them tips on which zones to play in which order to understand the story, and many of them have thanked me for it. In its current state, the format of the storytelling needs to be changed, because the railroad legacy makes it hard to make sense of.
REGARDING THE TIMELINE:
The events of Tamriel are linear in spite of the introduction of open world exploration. The alliance quest chains lead to Coldharbour, which leads to exploring the alternate alliance stories through alternate realities. The failed Planemeld leads to the Planemeld Obverse in Imperial City, which leads to members of the Worm Cult trying to continue building dark anchors in Wrothgar (along with other recurring characters from the other storylines sharing their exploits). There's even a journal in Wrothgar called
Birds of Wrothgar, that
clearly marks the year as 583, Orsinium being released in november 2015, one year after the official release of TESO. Not having enough food for the winter is also a recurring theme and cause for concern mentioned throughout the Orsinium storyline.
Going by this, players (roleplayers and lore fans in particular) have interpreted that time in-game passes with a 1:1 ratio with time in real life. After Orsinium, no other references to dates have been made, but with the constantly recurring characters and references to past events, for example the chain of events from the Prophet's final prophecy at the end of Orsinium and the dialogue of Tsatva-Lan in Cradle of Shadows, to Morrowind, to Clockwork City and to Summerset.
However, Leamon Tuttle, the new loremaster, has gone on to give the following statement:

I spoke with an employee of Bethesda myself, during a survey earlier this year, whom gave the following response to a suggestion I gave them:

To rephrase what they said, in-game time is relative to you, and you decide how the stories take place. This is,
in my opinion, a poor form of storytelling, and an even worse excuse to not have to do the game's primary content justice. It flies in the face of the timeline.
Take the Dragon Crisis. Dragons are in Elsweyr, even though they weren't seen for ages before. Why? Because Abnur Tharn released them from the Halls of Collosus, and I guess they've rapidly reproduced. Why did he release dragons? Because he was looking for a weapon that could end the Alliance War. Why does Tharn want to end the Alliance War? Because he's really not a bad guy.©
Wait... wasn't he kept prisoner in the Castle of the Worm, by Worm Cultists? Oh, right, we freed him in that quest,
Castle of the Worm.I understand that ZOS don't want to make players feel like they're playing the game the "wrong" way with the "play how you want" approach, but I think the idea that one can do so successfully is not just a folly, but delusional. There is a timeline of events, and I think that rather than attempting to do more one-year adventure storylines like
@bluebird highlighted in his thread found
here, the timeline and zone story progression should instead be clarified, to help players see how each zone's quest chain fits into the bigger picture.
HOW I THINK THIS CAN BE DONE:
As I've said, I think the base game's storytelling is fairly unwelcoming to new players, and that making all the content of TESO take place in 2E 582 is rather unfeasible. I therefore want to propose some ideas that might help make the base game's story both easier to understand, and easier to approach.
I think there should be an option to choose which tutorial and starting point you want to go with, but if you enter any of the base game zones without completing the original tutorial, you should be "forced" to do it. Maybe a Worm Cultist could walk up to your character and knock them out? This will help reestablish the game's main quest, and explain how players are able to deal with soul-threatening tasks in the base game zones.
I understand that it might be annoying to have to do the first base game quest when you really just want to go to your alliance capital to grab the pledges on your newly-leveled tank, but in the interest of introducing new players to the base game zones, I think this would be a good compromise.
I also think the main quest should only be playable up until the quest Council of the Five Companions, without completing your Alliance's storyline. That way, Vanus' message will arrive just in time when the player is told by their alliance leader that they have a message from Vanus Galerion, to then grant access to Coldharbour, and the Coldharbour storyline. Which is how they did the Season of the Dragon finale, which you had to finish both Southern and Northern Elsweyr's main questline to start.
I also think that all of a zone's story quests should be locked behind the first quest of the zone. This starting point should be highlighted for players in the zone guide, unlocking the quests after completing the one before. This wouldn't mean that you won't be able to explore Fullhelm Fort as I did back in 2016, but it would mean you won't be able to do the quests there unless you have completed the ones before.
DLC zones should be excempt from this, however I believe each zone should be given a mention of when it takes place in relation to the other zones. That way, if someone wants to play the zones chronologically they'd be warned if they enter a DLC zone that takes place after content they haven't done.
To also make it easier to understand the timeline, I propose the same idea that I pitched to the employee in the screenshot above; zone summaries. These could quickly recap the year of the zone's story and main events of it to catch players up on the events of Tamriel, and help give a clue which zone happened before and which comes after. The should also be available
AFTER COMPLETING A ZONE'S QUESTS. That way, you will avoid potential spoilers like the employee highlighted, and give players a recap of events after they are done with a zone. I think this would add a good enough structure to let players explore the alliance questlines without sacrificing the exploration aspect of TESO that was introduced by One Tamriel.
Let me know what you think of these ideas in the comments. Do you have anything to say about how they could be improved? Do you have the gripe with how hard it can be to explore the legacy content? Do you absolutely hate quests and questers? Constructive criticism is always welcome, as is civil controversy.