Well, this probably isn't the thread to start this discussion on; but I honestly do not think flares are op. They only shoot 600 meters or as far as the nearest cloud (which now a days is much closer). Anything within the flare is already in gattling range and can return fire on the flare shooter, so it doesn't give a sniping team a huge range advantage.
Flares are one of those things, that as Gilder points out, become really rewarding in higher level play. It took me a while of playing GOI before I ever figured out a reason to equip one, and I have new players all the time asking me what I use them for.
For me they increase the complexity of the game, and create this sub game of cat and mouse, where one team tries to approach unnoticed, another team tries to flare them, and the first team, knowing about the flares tries to approach in a place they don't think will be flared.
TL;DR Flares aren't OP, they add layers of strategy and complexity to high level play,