Radio Shack rebadged lots of products from outside sources, with the CoCo I/II being mostly a Motorala design for the AgVision terminal. The CoCo 3 is notable because so many of the improvements were driven by in-house processes. I wondered if maybe some of the people who worked on the CoCo 3's improved graphics were behind the Tandy Graphics used by the 1000 line but nope, turns out they went back to what worked for them and copied IBM's modes from the PCjr.
If you still have an interest in the CoCo 3, the port of Attack of the PETSCII Robots is coming along.
For me it was all about OS-9 at the end
https://en.wikipedia.org/wiki/OS-9
which had a decent C compiler at the very least. I was checking out everything I could about Unix from the public library and creating my own version of as many Unix tools as I could. In terms of OS, the Coco 3 was head and shoulders over anything else you could get up to that point. It even had a windowing system that was a lot like Plan 9.
At some point though I was frustrated with there not being a lot of software for it and I did a data processing job for my Uncle Bob that paid for a new 286 machine although if I knew how much value it made for him I should have asked enough for a 386. The 286 was a massive step up in performance -- in high school I developed a CP/M program for a teacher using a Z80 emulator that was 3x faster than any Z80 could you buy!