I wanted to point out this is the first time I ever finished a track in a single day (I know it's unpolished and messy but by my standards it's finished...)
I made some changes to my workflow because I was fed up of letting myself be hypnotized by 4 bar loops. So I downloaded MuseScore and did my best to write out the music I was hearing in my head before I actually loaded up my DAW. It worked a charm. Might be a good tip for others that struggle with finishing tracks?
I think you head the nail on the head when you said there were no IBM-exclusive chips. I think the openness of the system followed by the proliferation of clones drew a ton of companies and developers to the platform.
The IBM also looked like a business machine whereas others felt cheap. It may not have looked like much on first glance but they struck a good midpoint between the C64/Apple etc and the business-oriented minicomputers on the higher end of the scale.
I think the success of the 5150 was less about what it did and more about what it was and what that represented, particularly to businesses