I think the hardware was moving forward equally quickly, but there was a more dramatic spread between the low and high end of the installed base. People waited

I think the hardware was moving forward equally quickly, but there was a more dramatic spread between the low and high end of the installed base. People waited years between upgrades because computers were so expensive. At the same time, Moore's law really was doubling speeds every 18 months. When Wolf3D came out in May 1992, its minimum spec targeted the installed base of 286s, and a 50Mhz 486 was bleeding edge. When Doom was released in Dec 1993, you could buy a Pentium. (And if you kept it till '96, that Pentium could manage Quake at 320x200). I agree there was a bifurcation in the late 90s when 3D hardware acceleration arrived (see the colored lighting and texture filtering in the Q2 screenshot). Quake 1 was getting patched with hardware rendering up until Quake 2's release, likely the bells and whistles your friend showed off :)