The community is the valuable part; creators want people to find their stuff, users want to find interesting channels and its fans, etc.
If you evict the community to an outside site, will someone care if the video links starting point to Vimeo or another video hoster instead of YouTube? Probably a bit, but not that much.
Why would YouTube makes changes that make them more into a replaceable part?
I didn't suggest that you remove the community. Users have a stream of liked content, a list of subscriptions, etc. That's valuable on its own—just ask Pinterest. You don't need comments to make the experience social.
If you evict the community to an outside site, will someone care if the video links starting point to Vimeo or another video hoster instead of YouTube? Probably a bit, but not that much.
Why would YouTube makes changes that make them more into a replaceable part?