It's quite sad to speak about RPG and read "optimal build" in it. This is a "disease" at this point as RPGs shouldn't focus on combat so heavily to the point there shouldn't be optimal way to build characters.
I think that is mostly a balancing issue, which is realistically not 100% solvable. Having classes that are exactly even in terms of how good they are is near impossible without them beeing the same. So some things will always be stronger than others and therefore will result into more optimal builds. However i do agree, that the discrepancy of the power levels between different builds should not go so far that you as a player feel stupid for not picking the other class, because it is outright better in every aspect. Everything should have its strengths and weaknessess.
I don't think any developer intends to make a game with different schools or classes just so every player resorts to the same 4 classes because the other 10 feel so weak, that it is really difficult to play through. But to be honest i have never experienced a game, where a class was so bad that you had a hard time finishing the game with it.
I also want to go against the notion of optimizing as a "disease". I for one love to optimize around certain mechanics/abilities/spells and see how good i can make it and yes i even google euqip abilities and so on beforehand. For me the fun lies in crafting the build and see how it plays out in game and once i did a playthrough with that build, i try another one and so on. Perhapts its more the notion that a player knows that they are playing a suboptimal build, that feels particularly bad.
