If you quit YouTube then you also quit all the content on YouTube that isn’t elsewhere. The best solution if you still want to use it is to use 3rd party apps. Personally I would actually count that as having no reliance on Google in particular anymore. If a video platform owned by Google wasn’t the most popular then it would be another platform. I don’t think you should think of 3rd party apps as YouTube frontends, but rather, apps that scrape videos hosted on Google’s servers.
That may be true but if you’re using a frontend then you’re just trusting them with your data instead. Perhaps many of those could be run by people with even more malicious intent.
Unless those instance owners have access to someone’s google account data then I’m guessing they have no more data on said user than any other website they visit.