If you want to compare streaming services to Roon, you must give Roon the same access to content. Roon does it really well if it has access to content, just like all the streaming services
If you limit yourself to your relatively small library, it runs a dumber algorithm because it is limited to a small subset of music.
If you don’t want to stream, then I’d argue that Roon gives you something with local content, which is better than any of the streaming services, which ignore your local content.