If you didn't know better you might think the design of the 99/4A was the result of a drunken bar bet over making the most inefficient small computer design humanly possible. Somebody definitely held someone else's beer at some point.
70s industrial design: never attribute to incompetence what can be explained by bureaucracy. Source all of your parts internally from different departments with different priorities. The PC and the Apple 2 (and later Mac) worked because each was created by a small team using off the shelf parts. C64, Atari 8-bit range and the Mac later stumbled badly later when the team size ballooned combined with a closed system architecture, while the Amiga worked well with the small team approach and then, again, followed the same path.