I think Doom was the clincher... the one that stole the limelight from the Amiga. It was the game that caught people's imagination, and the poor old miggy had nothing to compare at the time. Breathless, Gloom, AB3D, TKG etc are good games (I have them all). Better in some ways than Doom, but they were too late, and really most Amiga owners didn't have the hardware upgrades (and still haven't!) to enable developers to play catchup. If the base Amiga had been an 030/25 or above with a hard drive, maybe we would have stood a chance.
Doom runs well on an 030, but isn't the Amiga version rewritten woth lots of optimised assembly code? And if not, as I said... how many Amigans had fast 030 chips at the time Doom came out?