I’ve been using JRiver for years, and I still use it to manage my music. It does a much better job than Roon at managing music. I copy my music and playlist from JRiver to a SSD and plug it into the Nucleus.
I have 30k+ music files, and I don’t use Tidal or any other streaming service. I want my music and my music only.
Roon is not all or nothing, there are many things that JRiver does that are MUCH better than Roon. Using both gives me the best of both worlds.