Sort of. If I'm not logged into google or they can't monetise my data or serve me ads then I feel I have 'de-googled' from a privacy and convenience point of view. Nevertheless, if I'm still using what they are providing then I'm not doing anything to support or legitimise google's competitors. I'm also still going to see the sort of content that is cultivated by youtube's algorithms and business practices.
Third party apps are great though, especially if they can support multiple video hosting platforms and download videos to view offline. Newpipe is a good example of this. I can quickly go between my youtube subscriptions and my peertube ones.