Hybriddization was made to allow more build diversity, and while it made the game much more forgiving for a poor build choises, it restricted a lot of highend builds for PvP and PvE. More casual players do enjoy thier bow-caster-tank builds in open world, while optimised PvE group tired from seeing another full group of arcanist dds, and PvP is mostly recovery sorcs now with ocational acuity warden added to the mix.

People tend to find and use most efficient tactic avaliable, and with reduced spec variables now, having a single meta build for each class is halved as the result of hybridization, reduced higher-end players ability to play the way they want. And for any new player that want to engage harder content there is only one "starter" HA lightning staff build to rule them all have a feel for ESO's PvE endgame. And for PvP there isnt one.

Why did every skyrims dragonborn transformed into stealth-archer over time? This game didnt had any online, scoreboard, PvP or anything, yet EVERY skyrim player did it (at least once).
Because its efficient, easy, and ... FUN. Winning is FUN. Stealth-archer in skyrim is so broken that any other build seems like self-imposed challange.

So what so different about ESO? is it easier?
Well, it depends on the content you do, but for the most part its much more complicated mechanicly then skyrim. And having 7 different classes also adds a layer to overall difficulty, also considering that classes isnt classic archetypes, they much more like heroes in some moba or hero-shooter, each having their unique abilities that cover them for offence, defence and utility. And then there is a miriad of sets and skills and scribing to customise your character even more creating a lot of room for build diversity, only...

1. Few select sets outshines vast majority of sets, some of them feels like direct upgrade of another;
2. Some classes have clearly superior class kit to the others for a certain activity;
3. Weapon cobinations have a clear favouite, 7/10 times you fight somone in PvP they will use dw+frost stuff, 7/10 PvE builds use dw/two-handed. Any build that uses staff will use lighning staff. For PvE daggers are clear winners for the front bar over anything else, except when you have to use range (which is super rare);
4. Classes lost a choise between investing in mag or stam, you simply use most powerfull skills avaliable.

So we are here with characters that akin to moba heroes in a MMO setting, so now we have to give each of them a role...
Moba games usually built heavily pronounced weaknesses into the heroes so they can synergise with each other. Lets say we have hero A that deals a lot of damage over time in an area, so he weakness would be enemy leaving said area, and now we combine it with heroe B that have an AoE root/stun and BOOM, we have a strong heroes duo that fulfuills one another.
And with eso, well... PvE dont have such issue, DDs have no health and usually dont have room for healing skills so they arent good at healing or tanking, tanks cant dps, and healers too, so you need to assign a specific role for every player in the group.
PvP? every class can be built to deal damage, cc, and heal for himself, so there is no weaknesses in that regard. So how do you create a group composition for PvP? Everyone can slot two group hots + burst combo, one can slot RoA + Turn evil and you set. And then trade RoA bombs until one of groups is wiped. No need to think of a target priority, all of the dynamic of "protect your key target" vs "kill their key target" is abcent.

"Play the way you want" brought us in a most restrictive meta ever, where not even every class have a single decent build. How can it be fixed?

TES games have a vast magic system. A spell schools, that isnt really flashed out in ESO.
Lets say we implement destruction,conjuration,alternation,restoration and illusion into the game. How? We already have destruction and restoration staff, so.. maybe add conjuration, alternation and illusion staffs? Alternation can be tank staff with plethora of buffs/debuffs and utilities such as pulls or stuns. Conjuration is utility + summons damage. illusion is debuffs + mobility spells.

So lets say we added the staffs, what next?
Add scalers to skills.
Lets say its crystal fragments, and it scales from our max resourse and highest damage type. Crystal fragmet is summonig of a crystals (probably soul gems from oblivion) to sling at your enemy and deal damage. So its a hybrid of conjuration and destrusction. Then we add to it a scalers which would increase the final damage of this ability depending on what weapon you are holding. So, lets say we have 1k w/sd and 1k stam/mag and our frags deal 10000 damage with a base scaler of 1x, then, equiping a conjuration staff will make the scaler 1.4x since this ability is primarily about conjuring shards - and now our frags hit for 14k, and with destruction it would be 1.2x and our frags would deal 12k damage. In the end ability is still usable with dual wield, but you can push its damage further by equiping the staff that corresponds with it scalers.
Or lets say its hidden blade, the blade is mostly illusional (since its hide your real weapon and looks transparent), so it will have the higher scaler with illusion staff like 1.4x, while also scaling from a bladed weapon (dagger/sword/greatsword, since it cuts with a ..um.. blade i guess?) like 1.2x, and then 1x from any other weapon.
This way we wont hard-restrict anything, but will help players build arcetype they want to play, and have a way to optimise for their chosen way "to play how they want".