^This
Pyro is great and anyone that disagrees in favor of Arsenal is fooling themselves. That little combo above can drop someone just as quick as any other class if you're smart about it. Some people might be turned off by the ramp up time, but I find it very satisfying. For example:
You spot a Sage on an upper level during a hutball match, shooting rocks at people and hurting your team. You throw IM on, and they ignore you. You throw TD on and they still ignore you. They only notice once that detonates and after you shoot an insta-cast fusion missle at them, and by then, they're done. I can only imagine the look of surprise on that kid's face.
Pyro is a thinking man's playstyle and if it's too hard for you, maybe you should try something easier, like minecraft.