It is true you don't need Roon to stream Qobuz. I listen in the car to Qobuz directly because Roon is not (yet) an option there.
I do not do this at home and would not want to do without Roon there. I find the Qobuz user interface clunky and very difficult to navigate--not at all intuitive. While creating playlists is do-able on Qobuz alone, modifying a playlist on Qobuz appears to not be possible (or maybe I just have not figured it out after burning a good bit of time trying). Roon provides a considerably easier and more pleasant overall experience. If Qobuz alone were the only streaming option, I would probably just go back to playing CDs.
To me, Qobuz alone is like trying to get from LA to Hawaii in a rowboat, while Roon (with Qobuz streaming) gets me there on a cruise liner.
YMMV.