I feel limiting one aspect of game play would not have the effect you are looking for. It would alienate bomber pilots, hamper small squad base takes.
Bomber pilots would still have plenty to do, and perhaps HTC could add more options. As for small squads, are you really suggesting that the offense/defense balance should be skewed by a method that allows that allows offense to easily deny greater numbers of defenders any fair chance of combat?
Perhaps the only thing worse than not being able to up in defense is taking the time to fly to a base and discover that the fight is destroyed. There are times I would pay perk points to be able to shoot down *friendly* bombers. As I continue to point out, the tool-shedder mentality actually removes fun for players on *both* sides, not just the defensive team.
I also feel if it was as big an issue as you lead us to believe htc would have changed something in the last 10 years or so.
Tool-shedders weren't such a big issue when I first started playing years ago. Fights could and did literally go back and forth for hours. Now I observe they rarely last more than half an hour or so before someone drops the fighter hangars.