What problems do you have with the youtube app? Seriously, I watch youtube videos almost everyday and the official app is working fine for me. Plus, they fully support smart invert colours now like Facebook so good work by google IMO unlike many third party apps that take ages to support new APIs.
The app itself is fine. Usage is fine, though I would argue that the video player itself should be improved from the current one (should make it more like the new in-house iOS 11 music player).
It's not a total hindrance to usage in itself, but I find that it lags in certain areas frequently. It definitely can use more polish, which I'm surprised hasn't been done given the frequency of updates they have pushed out.