Reduce it's size, currently it's too fucking wide, length wise I think it's fine, but as it stands the airblast's size is roughly still as absurd as it is in this video made by Sievseg
This is undoubtedly a disproportionate amount of area coverage, make the hitbox smaller. Additionally remove the soft autoaim mechanic where anything you reflect gets automatically redirected towards the crosshair, being able to nullify an enemy's damage should be more than reward enough.
Flame particle mechanics
We already have a histscan stream damage based class in the game, we already have a hitscan burst damage harassment class as well. We also have projectile burst damage classes, but what we don't have in the game, is a stream damage projectile based class. Think of old arena game's super nailgun/plasma guns but with afterburn mechanics, however with some concessions to make as well. Make the flamethrower particles have the exact same trajectory as the syringe guns, meaning it has a parabolic arc so "gravity" affects them. Remove rampup damage bullshit from the blue moon update, and make the hitboxes roughly 10 hammer units by 10 hammer units wide, this will require players to aim their stream of "projectiles" and will effectively kill WM1. To further prevent spam either make the flamethrower shoot in bursts of hitboxes, or make the pyro have to switch out gas tanks after 50 ammo is consumed. Since pyro finally has adequate range to his attacks either remove afterburn, or nerf it even further. And of course make valve get off their asses to fix that airblast particle glitch.
What issues will this fix? Pyro's range, pyro's inability to do consistent DPS, pyro's lack of aim in order to use his primary weapon, afterburn's annoyance and unengaging gameplay of racing to a healthpack, the general annoyance of fighting pyros in closed off spaces which has his blinding flame particles make him hard to hit depending on angle of approach. Moreover unlike the hitscan suggestion this makes sure Pyro does not intrude on anyone's turf or steps on anyone's toes. Pyro will not intrude into demo man's roles since his role is that of area denial via sticky spam, and his grenades on direct hit are still burst damage based. Pyro will not intrude into soldier's turf due to soldier still being projectile burst damage based, as well as having superior mobility options due to stock rocket jumping, the gunboats or airstrike.
In general pyro's role will be a new one of soft area denial, that can still be slightly negated by scouts, snipers and heavies. However this time if the pyro is good enough he can punish overly aggressive scouts, and he can at least harass heavies at mid range.