Q 1) - you'll always get more destroyed on turn 1 of 41 campaign as Axis as it's to simulate the surprise effect I.e. Soviet planes all lined up, no dispersal, camouflage measures etc. Afters wars started and a weeks gone by you'd expect basic measures to be implemented hence not turn 1 destruction.
Q 2) - from what I know and believe how things work damaged planes will get destroyed when the airbase is overrun and bumped. If you have examples this is not the case let me know. For example if you bump an enemy airbase with 50/100 planes then 50 should be destroyed when you bump it.
The air war needs work. It's recognised by all but it's a big task, bigger than some may realise, and it will be looked at in due course.
Yes I know you get more destroyed aircraft on turn 1, my point is air attacks turn 1 (75-85% of aircraft damaged/destroyed), after turn 1 you never get 2 or 3% of aircraft damaged or destroyed. If an airfield has a lot of damaged aircraft one would expect to see better results.
Playing against the AI, on turn 2, I' over ran several Soviet airbases that were damaged on turn 1 but I didn't see any reported increase in Soviet aircraft losses, one base I know had 80 damaged aircraft.