Maybe its primary fire could leave a team colored cloud of gas that dissipate after a couple of seconds. Entering this cloud would poison enemies, causing them to take damage over time. The primary fire wouldn't deal tick damage itself in the way the flamethrower does. It only applies the poison effect, so you wouldn't be able to run up to enemies and melt them, with or without crits. The airblast could be used to push the gas cloud towards enemies like how gas in WWI needed wind to push it towards the enemy trenches. So, the pyro would set up clouds of gas and push them towards the enemy team, causing chip damage to help support his team. Now how much chip damage is up for debate as well as the ammo cost for airblasting. Nevertheless, I think this could be an interesting option for Pyro.