you claim that people are saying stupid BS but even if i dont work at blizz its still easy enough to see that the classes are not balanced because there are more than enough ways to find this kind of information out
one of these would be to look at raid parses in raiding. if you look at the parses on warcraft logs for the classes currently in the game the difference between the top spec and the bottom spec is like 20%, which means people will feel forced to play some of the stronger specs, or if you play a certain spec you will be a lot less likely to get a position in a raid team because of the spec being weaker,
that is one definitive way you can see class balance is a problem, and adding more classes or more specs would make it even worse.
so saying someone is saying stupid BS when you clearly have no idea what your talking about isnt helping anything
its also worth pointing out that the top end content as it is right now has a limit of 20 people, and there is 36 specs in the game, so that means that there is always going to be at least 16 specs that are sitting on the bench, if you also take into account class stacking is a thing you can easy assume that somewhere between 20-25 specs out of 36 are likely to be sitting on the bench
and if there is more specs/classes added to the game then thats just going to dilute the pool even more meaning that classes will just get even less chance to shine in the top level of content.