Since I'm a huge fan of tiling windows managers and spend a lot of my time in terminal emulators as a power user I believe to understand his vision about computer usage and have a lot of admiration for what he and his colleagues were working on. But for the general population I believe he did not have the "right" idea (easy to say with almost 30 years of hindsight).
AFAIK Oberon was actually used by "regular people" at ETH Zurich for a long time.
(and a lot of people ran and still run their programs maximized anyway)
Biggest gripe was finding a PC with a 3-buttoned mouse in the uni computer lab when it was full.
Being able to select, copy, paste and execute without touching a keyboard was cool.
(We used it a bit in a 3rd year computer science OS course)
Why did Amiga, the series of computers beloved by artists and musicians, have overlapping windows and colorful icons?
To be fair, these things were computationally intensive at the time. The Amiga had a hardware blitter and very good color capabilities, so it could afford to show them off.
Likely these creators understood the importance of overlapping, draggable, resizeable windows for the audience, and the audience indeed enjoyed them. Same thing with the classic Mac.
If you tried a tiling WM, you realize that it requires learning, tweaking, and discipline. Those are expensive qualities to require from users; one should ask for limited amounts of them.
So "arbitrarily overlapping windows" and "fancy icons" as "cute but not essential" may be telling, but is probably not telling what you thing it does.