Interestingly in designing the 500 there was a decision not to use the designers from Los Gatos responsible for the 1000 but to use the core designers from the Commodore group.
This came purely because commodore wanted to cost reduce the A1000 and Jay said it was impossible to move a load of discrete components from the motherboard into Agnus while George Robbins was very vocal about how it should be done.
Whether Jay believed that or he was using it as a political way to get funding for Ranger is something we'll never know, but it was his mistake IMO. George Robbins had a back up plan to have the "Fat" in a separate chip if it couldn't be pulled off, but it worked out ok.
Haynie was with Commodore at the time working on the C128.. think he was their lead engineer at the time.
Bil Herd was head engineer on the C128 and he resigned when it was complete. Dave Haynie was then head engineer for low end products.
He wanted to work on the 500 but moved to the 2000 team.
Not only did he want to, but it was his job to work on the 500. George Robbins refused to let it go.
George Robbins managed to repeat this with the A1200, started under the Pandora project. Again it was very controversial, AAA was the official way forward for the company so there wasn't much support from the start and then it got cancelled and subsequently resurrected.
The motivation behind the 500 was a low cost model. Not surprised it has a C128 flavour so most likely a Commodore old hat designer and not an Amigan in truth.
The C128 doesn't look like an old commodore product though, it got it's influence from elsewhere. Supposedly the keyboard layout was "stolen" from the vt100 terminals they were using on the mainframe.
