It is not the source of the file that’s makes the difference to the performance of Roon. It is the total number of files in your library no mater where they come from. Roon stores a lot of information about the files in your library and is constantly needing access it. Hence the recommendation for and SSD for storage of the database.
The other thing that can require a more powerful computer is any kind of DSP you want to use. You don’t mention that. This can be even heavier if you are playing to multiple zones at the same time. What are your needs here?
This has some more background.