The instigating effect that diverged the timeline was some sort of technological innovation around 1983-1984 that allowed an instant leap in CPU speeds and memory densities by many orders of magnitude. The timing of the advancement was such that the IBM PC architecture was hopeless outmoded and soon died off. Apple retrofitted the tech into their Macintosh line, so they stayed relevant, but the Amiga was still in the design stage and so was able to build their new OS and UI around the enhanced capabilities. It went on to dominate computing for the next several decades.

Their version of Amiga Intuition was able to include photo-realistic VR, global networking, massive neural nets, and so forth, which all contributed to the cyberpunkness of the setting.

Not a chance, I think. Combine both and you still would not have beaten the sound philosophy, openness, speed, and flexibility of the IBM PC & compatibles. Ironically, to increase your chances massively, you'd needed to have enhittification (with its preference for locked-down rubbish antithetical to general-purpose computing) already dominating the market. Even as Amigas and Ataris were much more open than their cousin's terrible grandchild of today: Apple. A platform which many Amigatari nerdlingers of yesteryear gravitated to...

Also I was an Atari ST user back then, and loved it. But the Tramiel's didn't "get" software in the early days. They failed to make the right investments to keep TOS/GEM actively developed (e.g. as a Mac alternative) until it was too late (they hired Eric Smith to work on MiNT and then MultiTOS in the early 90s but they were already done as a company by then).

And then three fundamental hardware mistakes with the ST were:

1. not shipping it with the Blitter from the start so it couldn't compete on games, obviously with the Amiga but even with 8-bits of the time

2. forcing the ROM size down to 192kB so they had to size optimize the crap out of GEM before shipping (waste of precious development time), especially including tossing away all of GDOS (which had support for proportional fonts and printer drivers etc). A 256kB or 512kB ROM would have solved a lot of problems with what I'd think wouldn't have been an insane BOM cost bump.

3. Minor but long term annoying -- tying the cartridge port to only have 128kB of address lines. If they had given it 256kB or 512kB address ability their later expansion issues (OS upgrades etc) would have been much improved.

As for the Amiga, great machine but a) it cost too much at the start so failed to catch immediate fire (the 500 rectified this to some degree) b) interlace.