Sounding good with MIDI used to be hard. As long as synths and soundcards had a few MB's of samples, you sounded like a videogame at best.
Today, PC's have gigabytes of RAM and even today's synths carry multiple gigs of sample material.
Does MIDI sound as good as Realtracks? Yes and no, I think. If you like the playing and the sound, you're probably fine with Realtracks. But, if you think the playing is too heavy or too soft or the sound is too harsh or too mellow? Good luck changing that.
MIDI is still more flexible than realtracks. You have more options style-wise and with todays' sound libraries, you sound great, too.
In this video you will find a comparison between built in sounds in Band in a Box, 2 of my (freely downloadable) soundfonts and a Kontakt library setup. Though I struggled with mixes and volume, I hope you can hear what the differences are.
You'll find the Soundfonts here.