About synth engine...

Hi. I'm currently writing a piece to be played using the soundfont Blanchet 1720 by Soni Musicae (easy to download online for free).
I load it at Musescore synthesizer at the Fluid pane and it works nicely. However when I silence Musescore synthesizer, change the output to Jack and use the same soundfont in Fluidsynth via Jack it sound more bright and clear. I turned off all the effects on both synthesizers but Fluidsynth still seems to sound a little clearer.
The word "Fluid" in Musescore synthesizer gives me the impression that it is based on Fluidsynth. But if so, why is there difference in quality from output in Fluidsynth itself? Or am I wrong and Musescore synthesizer doesn't have anything to do with Fluidsynth?

(PS: These may look like audiophile questions, but the fact is that Musescore playback advanced so much in recent years that now it's possible to write high quality music on Musescore itself. For harpsichord, I simply add tenuto at notes to create legato (using 95% gap without tenuto), use no dynamics, create some arpeggi in piano roll and add some tempo changes (set to be invisible) to feel more human and it sounds very convincing. No need to use other sequencing or editing software. This why playback output matters in this case.)