Every time Firework hits an opponent, the delay gets shorter and the starting damage gets bigger. When a firework is made, it builds up damage for as long as it exists, starting up from the SFD (Starting Firework Damage). On the other hand, every time Rocketeer hits an opponent, his rocket delay gets shorter and his rocket's damage gets higher. He has to wait the rocket delay until he spawns another rocket. When a rocket is spawned, once it hits the opponent, it explodes and the opponent takes the rocket's damage.
A Kinetlarp simulation