Internal synthesiser features too much reverb
It seems the internal synthesiser (Edit->Preferences->I/O) is way too reverbed (at least on Windows) so that everything sounds a bit 'muddy'. Turns out that by default chorus and reverb are on for any new instrument, although turning them down only improves (IMHO) a little.
I would suggest at least setting reverb and chorus to 0 by default, as I think for score editing the clearer the sound the better (if one wants to do a 'realistic' midi rendering with cool synth they usually use a sequencer anyway...)
Even better would be to use a default synth (soundfont?) with no 'hardcoded' reverb.
Al the best