In any game that you will encounter, there will never be a balance unless it's so simple. Like Rock, Paper, Scissors maybe?
In any game you can achieve a balance, but I personally feel it has to be done at the game's core and foundation of the engine and gameplay, to include whatever various modes.
Because... the characters, classes, fighters, whatever they may be, that are conduits for the players - balance is going to be hard to achieve at the cost of forcing homogenization and stripping identity. That's why the balance needs to rely on the core of how the game is actually played in these cases.
Since even RoS still has huge imbalances between how long/mid/close range and pacing of gameplay is concerned, it will still adversely affect the class(s) that aren't tuned toward where the game is skewed. And by that I don't even really mean the classes themselves, it's more the builds actually, and always has been.
D3 is one track and super one dimensional. Unfortunately this hurts particular types of builds/classes BADLY, and it's only going to happen again in RoS unless they seriously do something about it. Build diversity will suffer once again, as the game's rewards are still only in one place or style of gameplay.
If it's not class balance people complain about, it'll be build diversity instead.
One thing they've seem to strike pretty solid at the moment is class completeness throughout, though. Every class seems like a much better package of skills/runes/passives being more realized than before, but I'm afraid it's likely overshadowed by the game's one dimension, which will probably funnel all of that out.