Ofcom are slowly getting their teeth back with upcoming regulation (3 decades late IMO), but in answer to "what would we really lose?", we'd likely suffer immediate tit-for-tat responses from the US if we attempted to meaningfully regulate or partition our media from theirs again.
I don't think anyone who has spent much time thinking about it sees the Russia/China/Iran firewalls as a bad thing, but we aren't them and we can't regulate our media in the same way.