About a year ago now I thought so too; that Mosaic sounded better than the same track played back via Roon (and even posted on this forum claiming so).
But in fact, they’re exactly the same - a local track played-back via Roon is bit-for-bit identical to that same track played by via Mosaic.
Perceptual bias is a real thing that actually effects our listening. The only way to know for sure if there’s real differences in the physical world is to measure it objectively - a platform like the dCS Vivaldi with it’s disaggregated components and features like Clone mode in the Upsampler, makes it very simple to objectively measure bit streams for differences.