Before it, you could claim that a 68040 was kinda-sorta keeping up with the 486 and that the nicer design and better operating systems of other computers made up for the delta in raw performance, but the DX/2 66 running Doom was the final piece of proof that the worse-is-better approach of using raw CPU grunt to blast pixels at screen memory instead of relying on clever custom circuitry was winning.

Faced with overwhelming evidence, everyone sold their Amiga 1200s and jumped ship to that hated Wintel platform.

Flat framebuffers and "powerful" CPU's also enabled easier software rendering (Doom/Duke) of 3d, compared to the Amiga where writing textured rendering for an Amiga is a PITA due to video memory layout with separted bitplanes spreading bits of each pixel into different memory locations (the total memory bandwidth reduction in 1985 by using 5 or 6 bitplanes became a fatal bottleneck at this point).

It wasn't really always full framerate though and the 2d chipsets did help in "classic" actiongames that were still much in the rage.

The Pentium further widened the gap, but at the same time consoles gained hardware 3d acceleration (PSX/Saturn/Jaguar) yet the Pentium could do graphics better in some respects (As shown with Quake).

Once 3d accelerators landed, PC's has more or less constantly been ahead apart from when it comes to price (and comfort/ease).

The Pentium is the first one, I think, that this didn't happen, because by then it turned out that people need a computer that can do what they are currently doing—but faster—much more often than they need servers.

The 386 SX was a crap, 16 bit wide bus IIRC.