While I'm not exactly playing with Denied Airforce, the Panzermon AAR with just captured equipment (where possible) is very similar to that concept, and it was especially like that in initial stages. It seems to me that as the amount and variance of what is given increases it also becomes more interesting especially in 1941 - I am really looking forward to using some of those new British and Soviet planes, especially since now there's a larger variety of them and they seem more valid including more tactical bombers and strategic bombers. It of course needs to be rare since otherwise Denied Airforce stops being Denied Airforce at all, but the balance achieved right now is about right I think, at least for General level - even if one would swap Denied Airforce for AA veteran entirely and not get upgrades/new planes beyond those extra captures or prototypes.
Looking at specific scenarios:
1. Dunkirk - probably the hardest to do with Denied Airforce and if no preparations were done in AO 1939 by the player, borderline impossible. Just some D.520 won't get the job done and the Fokker D.XXI is a bit of a meme.
2. Dover - much better, since the player just needs to provide cover for a few turns before landing and worst case scenario can use obsolete planes as barrage balloons...
3. Operation Mercury - Probably doable with just swarms of paratroopers and zero planes, but would be prestige draining and require setup.
Aside from those factors I think just the idea of giving players options is great for increasing customization, replay value and inspiring ideas. Even if it's purely cosmetic like the Toldi tank in 1941 which is stat identical to the German tanks also available and as such has purely cosmetic value.
If anything, a good idea would be to set these extra awards/captures close before those air only scenarios to make sure that this minimal support can be given to those who want it, even if it limits this to single mission use by limited supply. It was already done with the D.520 and Hurricanes, so keeping this trend seems fine.
