pyro can kill, just know your goddamn limits.
Don't rush in, light up/airblast/shotgun, if they don't see you or they are a heavier class light up/axtinguish.
Only time when I rush is against a setting up engie, sending back the engie back to the spawn along with his nest is worth it even if you die.
Also, know when to retreat. If you meet a heavy around the corner, light up/blast him back and run like hell. In the end, pyro is about making the correct decisions and having fast reflexes, not about godly aim.
Is it just me or is Soldier the only purely offensive class that TF2 classifies as such? Scout and Pyro seem to be more about distracting and injuring than just outright power.
It depends on medic support and overall teamwork. Any class can help with pushing...except for 99% of snipers :V