Very few guys are going to climb 29s to extreme heights. HQs will still be defended by those obnoxious little rocket thingies and 90% of the time 29s will be at Alts that will make standard interception easy.
Dont forget we have some monster high Alt. fighters in the game including the almighty Ta-152, "which isnt perked anymore". There are other planes more then a match for it too. Some perked, some not. Some post 30,000' speed numbers above 470 mph. If we ever got the Mig-3 that crop of high Alt. fighters would grow even more.
There would be an initial rush of B-29 sorties as everyone burned thru their bomber perks but that would sort itself out. Eventually your only going to lose so many 100 perk point bombers. Everyone of the bomber operations Ive flown have been in the 20,000' to 25,000' range. An altitude easily reached by fighters in the game.