Before taking his comments too seriously I think there are some crucial aspects you need to understand before giving value to Carmack's opinions.
Carmack was amongst the first of a new breed of game programmers with a decreased knowledge of computing technology. Before this most top game programmers needed to fullly understand what they were doing and how the actual hardware they were working with really operates.
Carmack grew up in the age of technologically very obsolete IBM compatible computers running a very flawed and featureless operating system called MSDOS (which was based on stolen source code of an almost equally flawed operating system called CP/M). There were more advanced systems out there like Apple's GUI based operating systems and more importantly with regard to gaming the Amiga computer which especially shocked Apple's head of Macintosh development at the time for its far ahead of its time functionality and multimedia power.
Quoting Apple's at the time head of Macintosh development regarding the past: "When the Amiga came out, everyone [at Apple] was scared as hell." Apple could not figure out how Amiga Inc could have created the Amiga computer which allowed advanced features such as a fully pre-emptive multitasking 32-bit GUI-supporting operating system with the ability to display thousands of colors and output high quality stereo audio at a time when CLI-only PCs could only beep and like the 2-color soundless Mac could only run 1 application at a time. The Amiga went on to become very popular in Europe as a multimedia and games plaform and for advanced niche markets which required more advanced systems such as at NASA for rocket telemetry, the special effects movie industry and early efforts with regard to virtual reality experiments (including military simulators). The IBM compatible PC took a long time to match the Amiga's capabilities and the underlying architecture was so very obsolete it was really a hell having to operate those systems directly.
But eventually simpler computer languages were developed which more and more hid the underlying obsolete flawed x86 PC architecture from a new wave of less knowledgeable programmers (compare this to translators). Fast forward to today you don't per se need to understand much with regard to computing technology to create a game with many multi-featured pre-baked development tools. For example basically even you don't need to understand anything with regard to computer technology, understanding the underlying architecture to create a fully featured game in for example LittleBigPlanet 2 and the true knowledge of many game “programmers” today don't really extend far beyond this.
John Carmack first received much credit with the release of the very popular game "Doom" at the time. This game greatly helped to put the IBM PC on the map as a gaming platform. This was some 8 years after the release of the Amiga platform. Many consider Doom as one of the first and most advanced FPS games ever for its time, although neither of those two statements would be correct: For example there was already a very advanced virtual reality FPS game called Dactyl Nightmare build with Amiga technology predating even Carmack's Wolfenstein 3D. Unlike Wolfenstein 3D, Dactyl Nightmare allowed multiple hight levels (going up stairs), included stereoscopic 3D graphics, motion control sensors for both hand and head tracking (for example allowing the gamer to bend his arm around pillars hiding behind them or looking above or below you by turning your head) and 4 player network play with realtime spoken microphone communication. (Dactyl Nightmare include Death Match and Capture the Flag modes, game modes still popular today).
Despite the facts Carmack received a lot of praise as Doom was one of the best games for in the home at the time, this despite technologically there were already far more advanced games and this technology significantly predates the arrival of Doom by years. Until the arrival of Doom the Amiga basically reigned home computer gaming and of course he was asked if he would create an Amiga port of his game. His reaction was that it would not be possible and this today underlines his technologically incompetence at the time as the easily portable source code of Doom was released to the public and now runs on Amiga computer configurations older than oldest compatible PCs can run the game (actually meanwhile those nowadays also run Carmack's Quake, which needed a far newer top level PC configurations to run than Amigas can through at the time available upgrades).
So IMO it's very important to understand where he comes from and the kind of games developer he actually is before giving too much value to his comments. A person like him needs technology familiar to him and requires not too much knowledge of how the platform actually operates (simplifications and abstractions).
