I think it takes significantly more mental extrapolation between frames and general adjustment to your eyes not receiving frames at as quick of a rate but if the frame rate is fairly stable the human brain adapts.

The brains visual processing is so powerful that the difference between 30fps and 144fps on paper is much smaller in reality, especially if your brain has already learned the muscle memory of “upscaling” a low framerate to work with its perception of a 3D environment.

Competitively, for games like arena shooters or rocket league the frame rate is real but for most games it is a matter of the smoothness occurring on the physical monitor screen or it occurring on some level of mental image processing. What someone sees who has let the mental skill of processing a lower frame rate atrophy is a temporary sensation like putting on colored glasses for awhile, then taking them off and seeing everything washed out in a particular color. Weird, uncomfortable, but temporary.

The real problem is inconsistent framerate where the clock your brain has gotten used to receiving new visual information with the arrival of each new frame of visual information is slow enough to be on the edge of perception but keeps speeding up or slowing down chaotically. Your brain can’t just train a static layer of mental image processing to smoothen that out. Time almost feels like it is slowing up and speeding down a little, and it becomes emotionally discouraging that every time something fun happens the framerate dips and reality becomes choppier.