Add to this the bad experience we had with Sourceforge, and I definitely worry it could be all over for GitHub if this is true.
Subscribers don't see videos from those they're subscribed to in their home page(a depressingly large percentage of the time).
Things like the YouTube inbox are so 'well' pushed to the background that most people don't remember they exist, let alone know how to use them for anything.
Recommendations are borked, and often consist of videos you've already seen ten times (maybe even ten times today).
Rules in general seem to applied based on how popular a YouTuber is/how much money they bring in instead of what they actually do on the site.
Fair use is basically non existent, or very poorly applied overall. Sometimes people are able to get paid off content they don't own and it's almost impossible to get it taken down/demonetised, sometimes content is claimed through complete lies by the claimant.
Google account integration means that any setup related issue can break large parts of the site. For example, I couldn't previously get Adsense on my account; not because I wasn't qualified, but because the account I used Adsense with and the one I used YouTube for were different, and the merge basically broke any chance of connecting them.
YouTube comment/channel moderation is really bad, with few tools leading to horrendously toxic comment sections.
And then there are various bits of the interface that make me wonder exactly who designed them. For example, you've got a username, display name and channel name, and all can be completely different from one another. Or conflict. This makes it easy to confuse or mislead people, since youtube.com/user/[whatever] and youtube.com/c/[whatever] can be completely different people/channels.
It's hard to pinpoint what exactly is different but the freshness of it is gone. I don't expect anymore to find anything super-interesting and the same old stuff that I've already watched is being suggested to me again and again.