The heavy gunner perk gives increased accuracy for your minigun. Do this go for the vertibirds minigun aswell?

I think so, also I can kill much faster using vertibird minigun

Vertibird

I saw a courser take one down and thought . . . wow the vertibirds are crappy

Yeah, the Vertibirds basically fall out of the sky if you look at them sideways. I think it has something to do with the fact that blast damage more often than not kills the pilot as opposed to the actual chopper. Put a single rocket into the forward airframe or cockpit and watch it spin out, hurling passengers every which way.