agree 100%
i will never understand how this was ever an argument against new classes.
was vanilla wow class design balanced, or any other expansion after that?
would there be a balance if blizzard would have never added a single new class but made all the other changes to the game regardless?
no, that would not have been the case either way, remove all the new classes or add 10 new ones, it makes no difference at all in terms of balance.
look at other games that feature multiple classes with very strict rules when it comes to casual and, more importantly, competetive pvp:
they all (or most of them) add new classes over time and there is not a single one with an absolute perfect balance
would you rather have LoL, dota2, rainbow six siege with only like 5 classes?
how fun would that be after 12+ years? (talking about wows life span)
a new class can be very beneficial to all players, if its a hybrid like a paladin for example, the least you would probably get out of it is another possible tank for your 5man dungeon group and shorter queue times (among a ton of other things of course)
so yes, add a new class with each expansion, hell...add 3 new classes each, go all out at this point...