I don't us .40 in a subcompact pistol, it's just too heavy on recoil. It's similar to shooting a S&W lightweight J frame in .357 magnum. Are you kidding me! That is an exercise in absurdity. Even the slightly improved ballistics(very slightly!) are not enough to warrant the increase of the recoil. IMHO, anyway.
9mm in a subcompact is just fine, and even some of the really light subcompact pistols(P*-9!), it is still too much to tolerate for very long.
Yes, some people can handle it. I can too, as far as a few defensive shots fired. But if a person is serious about his ability to use his carry pistol in CQC, then he/she needs to train w/ it, and that's where the heavy recoil problem will show itself. If it hurts to train w/ the pistol, then most will not train. That is a big problem. Each to his own, however.
Stay safe, All. Ofc.JL