I don't doubt the proprietary players best with the streamers they're optimized to work with. Whether Roon is optimized for the wide variety of streamers its used on is the question. No doubt the Roon interface requires more processing than the stripped down proprietary players, running more processes means more opportunity for noise to be generated. This doesn't mean motherboard generated noise has to affect SQ, my custom build has linear power supply dedicated solely for the processor, another for the motherboard, and the PCIe cards for various interfaces totally isolated via extensive on board filtering, clocking and external linear power supplies. Any noise generated by motherboard doesn't make it to the network port or usb renderer/port.
For individuals with streamers that don't have embedded proprietary music player software there are various music players available via subscription such as the Stylus which is available within Euphony OS or as endpoint only via Stylus EP. Others could then compare these proprietary players vs Roon. My own comparisons of these two is still ongoing, Euphony OS allows settings for Stylus I have yet to try.
Also, Roon likely has deepest pockets of all the music player software developers, means constant ongoing upgrades. One also should be mindful that streamer manufacturers using Roon are extremely likely to be working alongside Roon in order to optimize streamer/Roon integration, this would include attention to sound quality.
The fact the proprietary players embedded in certain streamers preferred to Roon doesn't mean Roon SQ inherently inferior. Roon users also not obligated to use any of the filters/volume leveling/dsp, fact is I turn every one of these off, I hear sound degradation with some of these.
I observe individuals claiming great sound quality with virtually all music player software out there, until an objective comparison directly comparing these music players with a variety of streamers is undertaken I'll assume all can supply fine sound quality.