In Control Center it will also show you which App recently used those.
So that’s not more fine grained control, but it can help you understand when someone is abusing the permission.
I've asked in the twitter thread if early adopters of iOS 14 could also check if any apps access the microphone while in background (even though they shouldn't have to by use case).
I have the suspicion that some apps listen into conversations to apply speech recognition and NLP for targeted ads and maybe even more malicious practices - though I'm guessing networks close to FB for example would have been smart enough to have turned off those "features" for their apps by now but maybe not.
Still, it would be interesting: https://twitter.com/musha68k/status/1276112945496428544?s=21