That doesn't mean it takes up more time though. It literally doesn't, since you've gotta press the buttons during loading/break. It's the loading taking up your time, not pressing three buttons.
Also, how is it gonna work between rounds if you don't manually do it yourself? They'd be giving us less freedom if they only allowed us to do it at Character Select.
I see were at the splitting hairs part of the argument. Well whatever makes you feel good.
Anyways to answer your question,
Simple, if you want to do during the match. Then do it, and it switches. And you can just also set it before the match starts to be the version you want before the match starts.
Also to be honest, it isn't giving you less freedom, its just letting the selection be done during the CSS which is... well better in all ways. And if you didn't want it to be that way anymore, you could hypothetically switch it before the next match.
So the answer is, they could do both things, and everyone could be happy, and it would literally hurt no one. And you arguing against QOL changes for no reasons other than " cuz" and that's dumb