Going pyro while defending last is quite popular if you are at an uber disadvantage because you can waste enemy's uber by spamming airblast. Although this strategy is pretty easy to pull off, there are still some things you can do to make yourself more effective.

1) Don't let the enemy know you're playing pyro.

If the enemy knows that the other team has a pyro then they might uber in a scout to kill you and then switch the uber to the soldier, or they can just uber the soldier in anyway and have the scouts focus the pyro as soon as they can. If the enemy doesn't know you have a pyro its way harder for them to deal with you. Try to find hiding spots so that you can surprise the enemy.

2) Get between the uber.

If you time things right you can get between the uber and airblast the medic away, leaving his target without uber. I find this to be way more effective than airblasting the pocket because the pocket can just fire rockets around you or at you, which sucks unless you get a pro reflect yo. Unless your team sux then the uberless pocket will be easily defeated 8)

3) practice your pyro dm.

If you manage to live long enough past the "spam airblast at the combo phase" then your dm skillz as pyro become pretty important, since you're pretty much stuck playing pyro you need to make the best out of it by reflecting projectiles, getting crit flares, etc.

I hope these tips help some aspiring right click spammers :>