Interesting. OK, I am using this as I rip a box set I purchased:
Is the problem in your examples the lack of individual performers for CDs/tracks? Not ideal, but you could manually add those missing elements from other sources (such as the booklet that likely came from the box set you purchased).
At the end of the day, if the metadata doesn’t exist in an electronic form, what would anyone else be able to do better?
IMO, the ultimate solution to this problem is a crowd sourcing mechanism that allows Roon users to share hand-edited data assigned to these tracks by Roon users. If Roon modeled a system after something like Stackoverflow, with voting, et al., the right data set would quickly materialize.
For now, for me, I am hand-editing tags in iTunes and importing into Roon. Show me a system that does anything better for box sets.