Being able to run framegen above 2x on AAA singleplayer games is a huge win.

Keep min mind framegen * does not improve latency * May increase latency (though depending on the game and how the integrate with reflex, that may not increase enough to matter) * Costs performance in it's own right, which isn't a big deal when you aren't GPU limited, but 4x framegen is not 4x the framerate, depending on the scenario it can be 2.5x, but 3x is more common.

At minimum, the time between when you input an action and when you see it is your base framerate. Reflex or what ever other technology Nvidia talks about for latency reduction is all about additional latency reduction, not going below what is possible. This means that if you're struggling to render something at 30fps, it's going to feel like crap when you 4 x it (or more likely, 3x or 2.5x it if you're already struggling), your actions are still going to be felt at 30fps or worse latency.

Ideally your base frame rate is 60 or even better, something like 90+ fps (so GPU limitations don't scew with frame pacing). Many games limit input handling separate from display rate at 60hz anyway, or even what the physics rate is, though it can get more complicated than that. But if you're struggling with 60, the extra overhead may send you down in base frame rate you're multiplying form depending on how your system is handling frame sync, so having good wiggle room will stop that from being nearly as big of an issue.

Additionally, if your monitor cannot display the framerate your running at, you're actually losing out by using frame gen beyond the refresh rate of the monitor. Think about that. You have to be able to comfortably handle the game at 60hz already, even if you could do 4x, you'd be doing 240hz, most people are not using 240hz framerate or playing games at that frame rate, 120 to 165? sure, 240? Not nearly as many. And having your frame rate not be a multiple of 60 can cause issues in some games (SOMA, some emulators, old games, some RPG maker games), so you might just be lowering your frame rate anyway (and having a base 12 multiplier can help with VRR which doesn't have to change as much to get better integer multipliers, 12 is divisible by 2,3,4,6, which is way more than 10 or 5 has, 120 hz has 2x as many factors as 165hz for example).

So:

Being able to run framegen above 2x on AAA singleplayer games is a huge win

is really more like ~3x or you're compromising on your visual fidelity, in which case, it's no longer "free frames", or you're using a 5080/5090.

The input lag is barely noticeable for singleplayer (some people say it's good enough for multiplayer but I haven't tried that)

Remember the input lag cannot go below the base framerate, + all the regular input lag you would have had with out frame gen. If your base frame rate is high enough, you're not going to notice much of anything.

for example I can turn settings to high with ray-tracing on with Cyberpunk 2077 and then max out my monitor's refresh rate at 180hz

3x60.