AH diversity and balance are just killed by 3 plane types.
IMO, the point is not whether CHOG, Spit or Nikki are a killing machines or not, the point is that these plane are over-over-overused.
Lets go to the opposite corner, imagine the arena full of C202s and C205s. Sooner or later you'll get bored of finding the same enemy plane types over'n over.
The same applies to Osty. When was the last time you saw M16s defending a base?
And now about the perks. IMO, Tempest is not much better than CHog in relation with the rest of planes. Now imagine the Tempest unperked, 80% of CHog pilots will switch to that bird for sure. 90% of Spit pilot will switch also, and, probably, 50% of nikki ones.
The perk system should be useful to keep the arena balanced and with enough diversification to make it funny.
IMO, having an arena full of Zekes is as boring as having it full of F4Us.
Now we have a perk base system for fighters: 152 50p, Tempest 70p, the rest 0p. A good idea should be to increase the perks from the base based on a demand system. More demand = more perks plus the base. Less demand = less perks plus the base. Same system may modify the ENY values.
This way the arena will balance itself dinamically.