From this interview, it appears that what he's talking about isn't throughput, it's latency. At 60FPS, ideally you have 16ms to put a frame on the screen which has reacted to user input. This basically means that the user "feels" a lag of 16ms between taking an action and seeing it appear on screen. Because that "lag" is equal to the frame rate, it's about as good as you can get, therefore everything is ideal.
Keep in mind here that LCD monitors & TVs also introduce lag, sometimes more than 16ms on their own. In this case (although not generally, Carmack cares a lot about LCD lag) he's ignoring any effects introduced by the LCD and pretending you're running on a CRT monitor, which has no lag.
Drivers are generally fairly efficient in that they keep the pipes filled, but they generally have latency issues. This means you can render stuff to a much higher quality, but there's a short lag between taking an action and having it appear on screen. This is a notable difference in attitude between Carmack and others: Carmack cares about your user input getting to the screen fast, whereas others care about maximising the pretty. If he's an old fogey, it's purely in that respect, not because he wants old fashioned hardware wrangling.
If you've played games like Battlefield 3 (or even Half Life), some of you will get motion sickness, where you wouldn't from a game like Quake. BF3 uses the full power of your PC efficiently (i.e. high framerates), but it treats your input as a second class citizen (i.e. high lag). Lag is also very important in things like VR or other biometrics. Obviously, from a gaming perspective, you get a much tighter feel for your movement when you have less lag.
This stuff is actually completely fixable in drivers, but it needs far more intricate and well thought out APIs. You can also often trade off efficiency for better latency. What I'm saying is that to dismiss Carmack is obviously a silly thing to do, but you also need to understand what it is he's saying.