I agree with everything that Herb as said but I will add a couple of things.

1-in order to get good sounding MIDI you will also need good sound sources. You will not get good results using inexpensive GM sounds. You will need programs like Kontakt, Samplemodeling, and others. The thing these programs have in common is that they are expensive. Thus better sounding MIDI comes from better sound sources and the working knowledge of MIDI. Not to worry as the MIDI learning curve is not that steep. The translation of actual instrument nuances to MIDI may take a little longer. The biggest advantage of using MIDI is that you can play what you want where you want much easier that with RTs. IMHO a good MIDI sound source under the hands of an experienced MIDI user sounds as good as RTs.

2-It is not an either or situation when it comes to RTs or MIDI. Many of us use both in our music. In fact I use mostly RTs when doing clients music. Even a track or two of GM sounds can sound good when combined with a few RT tracks. However replacing those GM tracks with better MIDI sounds will make a huge difference.

3-My music uses virtually all MIDI and most all of it is on the user showcase forum.

I hope this helps and good luck.

Doc-take it easy John this is just a sharp scalpel. It will not cut deep so don't worry.
Me-I'm not John
Doc-I know, I am!

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware