A roughly estimated comparison of effort in attacking and resupplying strats:
Premise: Strats are at 100%, attacker going to kill off the city and the ammo factory.
Assuming 2h total flight time for every sortie (I could present you detailed mission profiles, but 2h is a good approximation for this purpose) it would take that many "perfect" sorties (no wasted bombs, absolute coordination between palyer, no losses to AAA or enemy fighters):
B-29 - 3 sorties - 6 manhours
B-17 - 7 sorties - 14 manhours
Lancaster - 5 sorties - 15 manhours
While the B-29 assumption is quite realistic when only one or two very good buff pilots are doing it (I did it myself a lot of times), it's highly unrealistic for the 17 or Lancaster, which are going to have much greater losses and (with more players needed) a lot of coordination issues. For them we could easily triple the effort needed, which still would be on the optimistic side.
So in the end, it takes anywhere between 6 and 50 manhours to kill city and the ammo factory (side note: additional factories come at a huge discount, as the city stays down for 6h)
In contrast to that, assuming it takes between 5 and 8 C-47 sorties to fully restore the factory, we come to just over 1(!) manhour of work for the defending side to redeem the strat raiders work of 6-50 manhours.
(By the way, it takes the same 5-8 C-47/M3 sorties to restore ords on a base, for which the standard suicide porker was investing only 10-15 minutes!)
So bombing the strats, with it's already only subtle effect on the arena, is finally made totally futile by that, comparable only to HQ raids. And it's not even worthwhile in terms of perks or score compared to town center milking....