No class can counter now... I guess... I am just sad...it took them so long to make this horrible change that pyro can literally counter every class...check it out urself
http://www.teamfortress.com/jungleinferno/campaign.php
Pyro has become more of a generalist class than anything now. As someone who plays mainly Pyro the distinct change that I have noticed is that flame mechanics are now different, and this in turns causes me to lead more of my attacks than I would before. Airblasting was fixed so it was no longer bugged. You say that Pyro is OP now, but you probably have never seen a Pyro reflect rockets behind them or at their side. The best way to counter Pyro right now is the same way you could counter Pyro years ago. Just stop getting so close to him. Sniper got a rework on the DDS to be a direct counter to Pyro, and he's still just as good at taking Pyro down as he was years ago. As a projectile based class, you should already adapt to playing against Pyros even before the update. Just aim slightly lower and they either have to backpedal to avoid damage or walk forward to try to reflect. Scouts have always had the advantage of being incredibly fast and being able to dance around almost any class. The only thing you may have had a gripe with is that there are more Pyros, if you still can't counter Pyro you're probably in need of some practice.
Scout ~ Speed/Double Jump
Soldier ~ Aim lower or at walls/ceilings in corridors
Pyro ~ Backpedal while firing against them
Demo ~ Aim lower, charge your stickies
Heavy ~ Stop positioning yourself in spots where you can't see a Pyro coming
Engineer ~ Stop playing so aggressively
Medic ~ Stop healing people who blindly run into a Pyro's fire
Sniper ~ Play behind your team and you should never have to worry about Pyro
Spy ~ Eh. Play unpredictably. Ignite times were reworked so you should still be able to escape when you get nicked by a flame particle while cloaked.