Thing is, I prefer a system where some classes are less common than others, and the only real way to enforce that is to gate them somehow. High stat requirements are a convenient means of achieving this, meaning that if a player's concept going in involves playing a gated class that concept is going to have to be put on hold until-unless the dice co-operate.
Stepping back a bit, the idea of having a character concept in mind before roll-up night is the root of the problem.
It seems others did so as well, but not here.
What I'm talking about here could be summed up as options that are intended to be partially allowed in a setting; where the specific intent is that when those options do appear in play they will be uncommon and known to be so; reflective of the setting's general population where such things are also quite unusual. Some species in my setting (Gnomes, for one) are far less common than others, but playable if you happen to roll into one on a species-abundance table. Some classes in my setting are similarly gated, in this case behind stat limits, so as to enforce some degree of rarity.
Level limits are another means of gating class-species combos but nowhere near as effective and generally not worth it. Variable xp requirements would, I suppose, be another e.g. a Gnome Fighter needs 1.25x the xp a Human Fighter does to advance each level but a Gnome Illusionist only needs .85x; but that too is more work than needed and would provide, I suspect, a very sub-optimal end result.