Instruments

That's like leaving MS Word because you only installed Comic Sans.

The default soundfont is indeed a tradeoff of quality in favor of smaller size and less resources.

Consider using the HQ Soundfont (installable as an extention) or find any others to your liking and use those. See https://musescore.org/en/handbook/3/soundfonts-and-sfz-files for more information on how to use different sounds with MuseScore.

It might also be good to know that if high quality playback is your end goal, you might indeed want to use a real DAW in conjunction with MuseScore. It still is first and foremost sheet notation software.
That being said, one of the main changes for MuseScore 4 is a better audio engine allowing better integration with other sound libraries (such as VSTs)