I mix and match a few different guides myself, mostly between Dottz, alcast and Hack the Minotaur. I mix and match from
Those three mainly but also experiment with some other skills along the way. You have to for certain skills anyway because they take pieces from mages, fighters, psijic and undaunted lines and some of those take a while to build up. Also many builds use skills that aren’t unlocked until you level those lines up quite a bit. This means a lot of patchwork when putting together a new build for a while. I’m doing it currently with a MagDK build where I need late skills from both psijic and mages guild but it’s gated content so it going to take a few weeks to fully unlock everything. I ran into the same thing on the magplar I have been playing and still don’t have all the lines And morphs unlocked that I need but I’ve got a fun build that works by piecing a few different components together. It still pushes 30K DPS without trial gear sets while wearing blue jewelry despite missing some of the skills the build calls for.

And there is my stamwarden, you will find pieces of this build on about 17 different guides! This is my main character but each ability I have slotted serves a purpose. It also has gear sets for PvE and PvP is my crafter, antiquarian, quester and my trail character. It’s not great at any one thing but a solid enough cog in the machine of any good group. I found stuff that works for me but I understand that I have to keep certain skills up that provide major brutality and major savagery to get the most out of this build. Every slotted skill has a place and has to be used in a certain order with minor variations. This is the build where I learned the reason why the guides build a certain way and also the build that helped me understand variations. One that started as an alcast, morphed into a Dottz and started taking pieces of other players plus advice of guild mates to turn into something that was fun and effective to play in a group or solo everything that isn’t a trial or veteran or DLC dungeon.

In other words the guides are simply that, just a guide. They are meant to be a resource for you to learn how to play ESO and once you see how the pieces fit together and how the moving parts of the build need to be timed and executed properly than it will really click for you. Getting to lv50 is step 1, gear cap (CP160) is step 2, and step 3 is getting to CP300 where you start unleashing the potential of some of these builds. Understanding CP is a whole other animal too, but fortunately for you ESO-skillbook.com also has a calculator for it. The generic one will get you close enough to the ballpark by entering your class and role and it takes jump points into account. It may not be optimized for the build but realistically we are talking a few % here and there from the generic calculator to some super optimized guide anyway. Losing maybe 1K DPS doesn’t change anything by that point anyway. That extra 1K lost doesn’t make or break a trial run, not understanding mechanics is almost always the problem there, but do t worry about that now.

So play whatever build looks interesting to you. Choose the skills that look interesting as well but research why the guides choose certain skills and see where your preferred skill can slot in for one the guide is using. Or maybe understand why the guide chose one skill of the other. Does it provide and extra buff? Is the cost cheaper? Is the cast time instant or is there a long time to channel the skill? Is one an AOE for the same cost and better for fighting mobs but still as effective on single target? That’s what you’ll learn from guides.

Anyhow best of luck. I hope you find a build that works for you and is still fun to play. Some of the builds out there though highly effective are mind numbing and boring others are overly contrived and complicated. It’s up to you to determine the sweet spot.

It's perfectly possible to grow up in this game and discover everything yourself. You progress gradually from overland questing to public dungeons to more advanced content. Trying different sets, builds, classes is a major part of the fun and has kept me going for a long time.

What's different is, if you're perhaps coming from another MMO or for whatever reason you want to jump straight into group content / guilds and progress quickly up the ladder. This isn't the greatest thing, if you ever intend to return to questing. The better you get, the more frightfully boring and meaningless you may subsequently find questing, because the combat is so easy.

Thus, unless your goal is strictly endgame, taking a build from an endgame player - this includes Alcast and probably every single YouTuber - is honestly not great. These are people who often work with a minimum of sustain, be it due to their playstyle or the group compositions they run in. Their builds will be effective for what they do, but that doesn't necessarily make them the most fun. They will be OP for overland content, while they may paradoxically be too squishy or lacking in sustain in the hands of a new player. If you are competitive and you simply want to reach the highest levels of endgame as quickly as possible, while not becoming stuck in some blind alley and developing bad habits, then fair enough. Learn all you can and go with someone else's build. The upside is that you'll probably learn about group-oriented skills in the process, especially if you are a tank or healer, and your guild will thank you for it. However, if you are more of a solo player or you're still in the questing phase of the game, there is no need for any of that.