ways to fix pyro:
1) Add an "overheat" meter which, when full, would either have the pyro take burn damage or not be able to use fire for a short time. "overheat" should go on most if not all pyro primarys. the only primary that might not need it is the degreaser which should be tweaked a bit as well.
2) The degreaser should become part of the "
Fast Food Freak" set on the workshop and it should shoot scalding hot grease instead of fire which removes the afterburn from it and makes the fast weapon switching make more sense.
3) Make the reserve shooter for soldier only. There really isn't a way to change it to make it less op without completely changing the entire weapon. Maybe Valve could make a special reserve shooter type weapon for the pyro only.
4) Change airblast so it actually propels you away instead of locking you in the air making you unable to move.
5) Change the flare gun so it mini-crits people who are on fire instead of doing a full crit.
6) Change the axtinguisher so it either does mini-crits or swings slower(not slower attack speed but the time it takes to do the initial hit is reduced)
7) Nerf the dps of flamethrowers. Most of the time fire can take you from full health to zero before you can even turn around and the afterburn can take down 60 health on its own.
This is all I can think of for now but there is plenty more.