That bit about the Atari 800 architecture and display concepts is pretty interesting as it somewhat matches the stories that circulated between the ST and Amiga folks that the Amiga architecture was the real follow on to the Atari 800 with a discreet blitter graphics chip etc and the ST was more Commodore like in it's initial design.
Well the idea of what became the Amiga was actually born at Atari, coming off the 400/800 PCS's and their concept (Three custom support chips for graphics, sound and other management, a display list manner of generating the screen, etc.). The 400 itself was originally supposed to be the "gaming console with keyboard attached" until Kassar decided it wasn't a good idea to possibly eat in to the 2600's profits (which at that time in the late 70's was still struggling), so the 400 was instead positioned as a lower end "entry" computer to the more serious 800. After they were done with the design work, Jay and Joe had wanted to move on to do the next generation of what they did with the 400/800, and move in to a 16-bit 68000 based machine. Kassar wouldn't do it and Jay quit, Joe stayed on to at least go up through the launch of the PCSs. Once Hi-Torro was started up, Joe joined Jay there (as badge number 2) and they continued as they would have at Atari. The irony is once he was done doing his design work, Joe contracted back to Atari to work on the expansion system for the XL series computers (1090 XL) and was there during the whole split. He had to keep publicly quiet for a lot of years about his involvement with the Amiga because of the lawsuits.