I think the most useful flexibility is for parents to do more specific categorization, eg allow violence on netflix but not youtube, block some game that would

I think the most useful flexibility is for parents to do more specific categorization, eg allow violence on netflix but not youtube, block some game that would be allowed, request access to something that wouldn't, set time limits and times of day, etc. It's easier to enforce this stuff on the client than try to send the relevant parts to an app or site, but yes there are times you want the latter too.