Well the thing about balance on a competitive videogame is that, even if something is unbalanced that doesn't make it unfair. As long as people have access to the same options, or like in asymmetric maps you alternate sides and play multiple rounds it's fair for competitive use.

What balance is about is making competitive play -interesting-. If competitors see that some character or weapon or strategy leads to an advantage some will gravitate to that strategy. And when too many people do it things get tweaked to make that less advantageous.

The developers do their best of course with play testing before a release, but after they get a ton of data to look at from people actually playing the game. Though generally they try not to make sweeping changes as that can lead to even more things going out of whack. A higher playerbase tends to find things the developers missed/couldn't predict just from the sheer quantity of people trying stuff out.