Downloading a handful of videos you personally care about is surprisingly affordable as a hobby. Mirroring and archiving the entirety of youtube is not.
Personally, although I couldn't say it was a hobby, I don't watch youtube on youtube anymore. Every youtube video I watch is downloaded first and viewed locally. I can't recommend it enough. Zero youtube comments, zero recommendations, VLC is a far better video player, Google has no idea how many times I've watched a video (or parts of it) or how I felt about it, and I never have to worry about videos I find valuable being removed. As long as I keep backing them up, I'll have them for as long as I care to.