We’re aware of an issue that can cause processing speeds to be a bit higher than expected with internet radio streams. This is a display problem, does not reflect actual increased usage, and only happens during internet radio playback. Its still be investigated but we are actively working on it.
As for the other questions, just keep in mind that you’re looking at the processing speed for a single zone processing on a single Core, and that this is only measuring the time spent processing audio–not the time spent fetching it or transmitting it to your audio device.
Roon also does work in the background like audio analysis, metadata updates, syncing your TIDAL library, maintaining network connections with audio devices and remotes, and keeping the user interface up to date. So just note that you’re not really comparing apples to apples here.