I've written code for Apple ][ hi-res graphics with it's odd interleaving and understood what I was doing. I've done (a little) Fortran77 on a Cray-YMP. I've done low level graphics, from 2D lines to 3D projections to mip-mapped textures on a CPU and bashed the results into a manually double-buffered framebuffer. I've written shaders for procedural texture mapping and phong shading (don't remember much about it, but I know I did it). I've written code to use various versions of SSE code on Intel chips, with runtime detection of capabilities. So I'm reasonably familiar with graphics and parallel operations.
I'm also familiar with iD software. I downloaded a version of Wolfenstein 3D from a General Atomics server back in 1992. I've played multiple versions of Doom, Heretic, and Quake. I've followed Armadillo Aerospace.
Which is to say that I've not only experienced the amazing things that John Carmack has put together, but I've done similar things (albeit without the commercial success he's had). But you know what? Some people just think differently. I think I follow what he's saying here, but it never would have occurred to me to do texture mapping that way.