Only if you limit yourself to bombing town centers. If you want to hit anything of value you expose yourself to risk. Even Lusche loses bombers, as he recently noted only the Mosquito Mk XVI was self sustaining for him. He lost perks on the B-29s and Ar234s.
I had one of the best sustained K/D's of all players in the 29 in the age of the central strats. Yet on 265 Superfortress strat runs I lost a total of over 3500 perks due to combat losses, disco and similar non-combat losses not counted. A typical B-29 run on the strats yielded only 2-6 perks , due to it's OBJ of 2.
Even when only milking town centers it's difficult to sustain your perk level. It's still only 4-8 perks per mission, and at 100 perks nominal price it takes a lot of milk runs to make up for the loss of even one Superfortress-