Designers were a tiny minority of computer users back in the heyday of Amigas, and they're still a tiny minority of computer users now. Designing for print on computers back then was as much a nice activity as using computers for video post production. So if the Amiga sucked at printing, that was not what held it back from succeeding, as desktop publishing was just in its cradle back then. In fact, as an avid Amiga user back in the day, I never ever heard anyone complaining about the Amiga's printing chops.
These are the kinds of arguments against the Amiga that I actually heard: "Who would ever need 4096 colors?" "I don't need to use all those sounds" (coming from IBM PC owners whose computers could only display 16 colors and only produce bleeps and blops for sound).
The Amiga's real forte was games, pure and simple. It was a monster of a gaming rig, for the day, and a ton of gaming innovation happened on the platform. Gaming was a pretty mainstream activity for computer users even then, and Commodore completely flopped by not marketing the Amiga as primarily a gaming machine.
Back then almost everyone was still designing for print, and the Amiga just wasn't cut out for that. It was a multimedia machine before there was any way to distribute multimedia to anyone else than other Amiga users.
Video production was a niche that was compatible with the Amiga's design, but working with analog video wasn't going to be mainstream ever... and for digital video, the Amiga was fundamentally underpowered.