IMO, the only real purpose of the perk system is to protect the arenas of plane overusage.
Plane usage is mainly based on plane effectivity for each pilot. Some of you will say, hey 109G10 is far better than SpitV and it is well underused. You are wrong, 109G10 is better only if driven by a competent pilot while SpitV is far better for the average MA pilot.
Based on this "theory" and based on the actual level of our pilots, SpitV is far better plane than 109G10, and cause that, SpitV is overused in comparison with any "potentialy" more competent 109.
So, IMO, planes should be perked ONLY based on the plane usage. For example, perking the TOP TEN used planes. More usage = more perks.
If your preferred plane is perked due overusage, there are always more choices that will fit your flying style.