Better yet, we could just separate the arenas for perks, and ramp up the perk multiplier when out numbered. Say you've got 50 on, and everyone else has 75, then your perk multiplier would be something like 2. Or hell, maybe even 3. We could play around with the numbers, see where the right balance is.
Would just encourage the perk seekers to fight, or even switch countries. Perk prices also need to drop faster when you're on the lower side. If together the enemy has more than twice your numbers, you need to be looking at 100 perk 262's in the hanger, 50 perk King Tigers and B-29's.