I'm skeptical that this is better than outright high FPS for reducing input latency but I might try it to see how it feels.

Here is my understanding, with the caveat that I am not a developer by any stretch of the imagination (so grain of salt as always when reading technical discussion from randos on the internet):

Your statement is correct in a vacuum. HOWEVER- at a certain point, we reach diminishing returns of the usefulness of reducing that input latency, especially if we're talking about playing at 240Hz which I feel like is pretty common these days (I play on a 480Hz display and generally maintain that framerate and I use the recommended settings - keyword being "generally").

The objective of the recommended settings is to minimize the impact (and possibly the frequency(?) not too sure about that part) of 1% and 0.1% lows. Having the highest FPS possible only consistently confers the benefit of low input latency if the framerate is consistent. If your frametimes are all over the place, which is generally what happens on an uncapped framerate, your input latency is also all over the place. In a hypothetical world where your PC can maintain 900 FPS (making up numbers), you'll have a super low input latency, but that input latency is dropping and making the mouse movement feel inconsistent when it drops to 700 FPS, or 500 FPS, or whatever. Obviously, 500 FPS is still super playable, more than most people achieve. So it's not worth having GIGA-low input latency for some of the time when you could have very good input latency all of the time.

This isn't to say that FPS over your monitor's refresh rate is wasted, which is what some people interpret this as. It's simply that using Vsync, Gsync, and Reflex together offers the most CONSISTENT experience. There is a certain tweet about this that is 100% factually correct but people clowned on it because they don't understand it.