>>95898532
And I know, you're going to say 'But that could all just be fluff rewrites'
Sure it could.
But I could also do something quirky with the setting and split, I don't know, Fighter, into three separate classes, Dervish (Two handed fighter), Bandit (Fighter-thief) and Taureg Warrior (Horse Fighter) or something and having actual backing mechanics for it (and give them trade offs) lets me pre-build the campaign and have the appropriate input I should have as GM on where things go.

What if I want to build my own custom races for the setting? Maybe brass men from the city built by Solomon?
That's another layer of complex-bullshit in and of itself.

Modern games have put the cart entirely before the horse by making it so the GM have complete control over everything except character gen.
The reality, at least I feel, is that the GM should have the most influence during character gen since characters should fit to the world and be a natural part of it.
And then once the players are out of character creation and into the world you then it's their show from that moment on with them steering where things go and what happens.

Like I said I'd never let my players use the custom class rules.
But that's not what they're for.