This is a recurrent thread- works like this:
Since engine overheat, freezing components, and other random calamities are not modeled, the planes all perform in a perfect environment. The B17 benefits the most here because of its turbo engines and generous wing area. Couple that with the laser-accurate bombsight that requires no zeroing in, and no ordinance drift, and you have a weapon that would make Stealth bombers look like slingshots.

That being said, it also seems to me that fighters cannot approach their theoretical ceilings. This results in B17's that cannot be intercepted above, say, 33K. Interception below that alt is possible IF you happen to be in the right place and IF you can kill in a single pass. Once the B17 gets a little alt and separation, he will walk away from you. Believe it or not, all they have to do is set autoclimb and watch you wallow behind them for an easy kill.
I agree this is not a good situation, and it potentially could upset play balance, but thankfully its abuse doesn't happen all that much.
When I see countries do this, then announce on open channel taunts "haha, we are so good" I just wonder how they would view it if 20 38K buffs ranged over their entire country and bombed their ammo, city, radar, fields- everything- to rubble while they tried vainly to put up some kind of defense. That could happen on any night, every night.
One squad ran a more historic approach to a raid the other night- ran buffs at 25K and had escort. They were successful, none of the defenders complained, and a good time was had by all. Would have ruined it to have brought them in at 35K, wouldn't it?