Maybe it's not the fact that the rounds are unrealistic, but that we can use as many of them as we like resulting in unrealistic loadouts.
What happens with DeWilde for the RAF can be reproduced with M-shells for the Luftwaffe. In reality, there wasn't unlimited supply of the "best" ammo types and pilots were forced to mix and match due to availability concerns.
Maybe a set of realism options down the road can help us with this. Having some preset historical loadouts as well as the ability to change them, but with some restrictions, would be the way to go. For example, restrictions could be to the tune of "x % of such and such rounds" or "X of such type of rounds in every 10 rounds total".
From what i've been seeing thus far, flying with the default loadouts doesn't produce results that seem unrealistic and this leads me to believe that the rounds themselves and the aircraft DMs are not bad at all. That's why i'm thinking that maybe it's us "gaming the game" that results in too many explosions