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.
With grayjay (assuming you use Android) you can follow creators and not platforms.
Able to access quite a few different services with just 1 app
In theory yes, but in practice Grayjay doesn’t really work that way. I think for it to work as intended, the creators need to actually create a Grayjay identity and connect it to their accounts. Which literally none of them do.
Grayjay just let’s you find creators only any platform there are plugins for. If a creator is on twitch and YouTube for example, it’s really just up to you to decide if it’s the same person when looking at the search results.