Tbh, there is no right time to balance. You don't know what kind of ridiculous stuff will come out within the first few months, and honestly, it sometimes doesn't take a whole half a year to figure out something is wrong. It sucks that the game comes out 2 months before EVO, because the game being displayed is so raw. We saw what happened at EVO with Injustice (not to discredit KDZ at all, because dammit he still was the Superman to put it all together that fast lol). Sometimes you can see the bullshit right away lol.
As far as a method to balance, in all honesty, the "buff the bottom only" method doesn't really work as you would intend. For starters, sometimes the top is just broken and has stuff they shouldn't have, such as one option that basically dominates the cast, or something that invalidates the way the rest of the cast has to operate. Also, with just buffing from the bottom, balance is already super delicate and, unless you precisely know what it takes (you likely won't), it may take hefty buffing to make a difference, and there may be things found that pushes those buffs far beyond what was expected, which just creates a new top that's broken.