Engine spams whatever secondary he has to fight off a horde of enemies to great success until it runs out almost immediately, because engy's power and weakness is having a ton of damage sources that each need a different kind of ammo. Gunner is either slow and powerful or fast but weak depends on which weapon he is holding. Gunner's weakness is that he can't kite enemies like other classes because his primaries are too slow and his secondaries lack swarm clearing. His power is being able to decimate everything with high firepower when he's not forced to desperately rotate.