Sure, WB was OK for 1985-1987. What about 1990 with 2.0? Compare WB 2.0 with the competition. The fonts are ugly (topaz got worse!) the new icons look like crap and everything looks dull and unprofessional. They could easily have kept it at 4 colours and made it look nice. And if they had an awesome 16 colour WB in 1990, maybe Amiga would have sold more ....in the years they screwed up and delayed AGA while competitors had more colours.
Edit: I'm talking about the "professional" Amigas here, not the "game" Amigas like the A500 (which wouldn't lose sales because of the crappy WB look)