You took the best armed and one of the fastest bombers, moved it up to an altitude that effectively removes it from gameplay. And from this maximum safety you simply dropped 10 tons of bombs on objects.
Much could be said about earning perks in bombers. But to me, this time 1.5 perks sounds about the right reward for that.
The B-29 is a plane to burn perks, not to earn them. It's a plane for 'maximum effect'.
In my opinion, it's bad enough that the two other perk bombers can easily pay for themselves.