I think the main reason of perking is to stop the spam of something. It doesn't work for the T-35 85 because the price is too low and GV perks are very abundant and how good the T-34 85 actually is for the price. I think some people would think twice about rolling something like the Yak-3, P-51D, or Fw 190D-9 if there was a nominal cost to it (even if it were 5 perks as a base).
With the question of Tempest vs. D9, the Temp is pretty much better in every way...it's faster, can turn better,, can accelerate better, and has a more lethal gun pack.