So arguably you never need frame gen for a game, since it only really works when it’s already pretty nice.
Framegen is also a good fit for low-end hardware like the Steam Deck, which can hit 30 or 45 FPS in stuff like Elden Ring but is far from the max 90hz of the OLED model's panel. For a handheld, trading a bit of 720p visual clarity for locked 90hz gameplay is a solid trade if you can get it working.
How about if the two frames are 100% identical?
Does either of these situations differ substantially from what is being discussed, wherein the render pipeline can only produce a new render 45 times per second?
it's input lag that defines experience, not frame time. I am comfortable with 30 FPS (sometimes less frames even fits the style of the game, e.g. Dishonored 2, Clair Obscur) as long as the game responds instantaneously.
https://youtu.be/f8piCZz0p-Y?si=OLq9iZUjuRMYKPDo
If you have never heard of it, the basic idea is that you make low FPS feel responsive in first person games by having the mouse motion warp the existing frame independently of when a new frame is actually rendered.
This could be combined with some AI techniques to help sort out the edge artifacts you get from this.