Commodore so slowly and ineffectually improving on the OCS didn't help, but the original sin of the Amiga was committed in the beginning, with planar graphics (i.e., slow and hard to work with, even setting aside HAM) and TV-oriented resolutions/refresh rates (i.e., users needing to buy a "flicker fixer"). It's like they looked at one of the most important reasons for the PC and Mac's success—a gorgeous, rock-solid monochrome display—and said "Let's do exactly the opposite!"
Iirc interlaced display and 6 bitplanes were a compromise to allow color graphics in 1985 with the memory bandwidths available at the time.
If it's a sin or feature can of course be debated but I remember playing games on an Amiga in the early 90s and until Doom the graphics capabilities didn't look outdated.
By 1992 with AGA however I agree, flicker and planar graphics(with 8 bitplanes any total memory bandwidth gains were gone) was a downside/sin that should've been fixed to stay relevant.