The interface he produced for that checkout system, the naming conventions he chose, the nature of state encapsulation, the testability of it? Yes, I believe Carmack would produce _better_ code in all those things than the median programmer every time.

There is much more to 10x than how many lines of code you can produce. A monkey on a keyboard can type faster than Carmack but productivity is not assisted. No one is arguing that a 10x programmer is more efficient by way of swift fingers.