try to be a "good" pyro without using the degreaser, axtinguisher, or flare gun.
pro tip: you cant
Ambush the enemy, defend engineer buildings, spy check. Just by simply igniting the enemy and running off before they can get a shot on you is doing a lot, considering most of them will fall back for health and be weakened giving your team an opportunity to push. You can do all this with the default loadout.