> I don't know if the dominance of the PC was a foregone conclusion by 1985.
I firmly believe it was, as it's the philosophy (i. e. the open architecture) that gave it such a headstart that the competition couldn't have catched up. Keep in mind what an open architecture really means in the world, i. e. not just the West.
> Failing the growth of that market in this counterfactual world arguably the A2000 and a bridge board was probably the first Amiga that could have seriously taken-on the IBM PC.
Pitting an already well-established and rapidly expanding open architecture and Commodore's first foray into an open architecture against each other wouldn't have, and indeed didn't, play(ed) out in the latter's favor.
The A2000, a workstation-class machine, arrived in March '87. Too late. Around that time Compaq had already sold around 25,000 of their first Deskpro 386 machines, which hit the streets half a year earlier. According to Michael Geran of E. F. Hutton & Co., Compaq sold 90,000 Deskpro 386 computers in the second quarter of '87 alone.
The bridgeboard was an option for cost-conscious operators, especially those with small businesses. They were well-received especially in West Germany where the A2000 sold well. Their limiting nature and performance wouldn't have made them relevant.
> I think a stronger Amiga marketing presence could have killed Macintosh.
That is an intriguing possibility!