As I understand it, the design intention is for it to be viable for players to play with defensive ground support turned on. So I have been trying to do that. Obviously HLYA is great with the air, so a game with him is a good opportunity to put it to the test of whether that is viable or not.
HLYA apparently had some settings wrong for his interception in earlier turns, which he has now corrected.
Anyway, so for during Axis turn 4, I had air support enabled selectively for certain Soviet HQs, but not for others.
This means that in some battles, Soviet air support flew, and in others it did not, depending on whether the Soviet unit being attacked was under a certain HQ or not.
First of all for context, here are the total air losses for the turn:

So 875 Soviet planes lost for 44 German fighters, about a 20:1 ratio, and nearly as lopsided if one does not count the Soviet bombers, since most of the Soviet losses were fighters.
HLYA did 30 attacks during Axis turn 4. Here they are, with battles sorted by the # of Soviet bombers that joined:

Circled in red are the 10 battles where Soviet bombers joined for defensive ground support. And circled in blue is the one single battle where Axis fighters joined the battle, but Soviet bombers did not.
So, what you can see from this is:
1) In fully 100% of the battles (10 out of 10) where Soviet bombers joined, Axis fighters intercepted them. There was not a single occasion when Axis fighters were unable to intercept.
2) In only 5% of the battles where Soviet bombers did NOT join, Axis fighters joined.
There is also another related issue:
3) I am not completely sure, but I think that Soviet bombers joined for either every single battle with an HQ where I had ground support enabled, or close to it.
My question is, are these 3 things WAD?
#1 is the one that seems the most questionable. Even in a modern environment, with modern radar, a 100% interception rate of enemy bombers seems on the optimistic side. Currently in the real world 2022 war in Ukraine, as far as I am aware both sides have conducted bombing missions without being intercepted, despite modern radar technology. As far as I know, the intent and what is realistic should not be that interception works 100% of the time for WW2 on the eastern front (especially in 1941) (???)
If interception works literally 100% of the time, that seems to make it not particularly viable to leave defensive ground support on, even if you are limiting it to only be turned on for some HQs, because you will simply get your planes shot down too fast, and since there will ALWAYS be enemy fighters, your bombers never get in a decent un-interrupted bombing run.
#2 is maybe a bit less weird. I suspect it might even have been a case where he had "ground support" enabled and the fighters joined as "ground support," but where I did not have ground support enabled for that unit. But still, you might think that if enemy fighters were so hyperactive that they appeared 100% of the time to intercept enemy bombers, they would also end up accidentally showing up in the wrong place and wasting fuel and appearing at least some of the time over battles where no enemy bombers showed up, due to command and control failures of varying sorts.
For #3, it also seems implausible that Soviet bombers/fighters would be well coordinated enough that they would be able to show up for air support in every single battle, without fail, for the HQs that they are supposed to be supporting. Surely at least some of the time, there would be a request for ground support, but no Soviet planes would show up, due to various failures. I am not completely sure in what % of battles where I had ground support turned on my planes joined, because there is no easy way to sort through them by HQ, but I think it was all or most of them.
I don't claim to be an expert on the air war, either in game mechanics terms or historically, but it seems to me like there ought to be quite a lot more cases where planes randomly show up on one side, but without the other side also showing up, due to the lack of good radar, and coordination/command and control failures of various sorts. I would not expect, for this historical period, for Axis fighters to be always 100% on the ball (or for Soviet bombers to always show up when requested).