If an airbase has more than 2 damage points would therefore be 3 or more which means it’s not functional at all.
I think 3 is too restrictive.
I would be ok with trying a house rule that requires:
1. Air Base is completely damage free for any extra movement range period.
2. 3 plane types could move an extra movement point; not unlimited… So, 3 bombers, 3 tacs, 3 fighters…ect.