The FPS and rolling shutter aberrations have little to do with each other.
1 FPS would still have the same issue.
The 40 FPS on the R8 and R6 II are quite useful for most moving subjects because the speed of the rolling shutter is fairly quick.
It is the R7 and R10 that are problematic but that is made up by them both having 15 FPS mechanical.
People seem to have it in their minds that stacked = fast and nonstacked = slow.
It is just one factor in sensor speed.
Canon has cameras with nonstacked sensors that are quite capable.
They do to the photographer.
From a feature point of view, a photographer is going to want to shoot at 40fps with fast moving subject (like a bird in flight). No one in their right mind is going to shoot a burst of 40 images if the subject is static. So the fps and rolling shutter aberations have a lot to do with each other.
Currently the photographic narrative is this...hey here's a camera (say a 6DII) that can shoot a 40fps electronic shutter. It's completely unusable and you will get messed up images with anything that's moving a lot. OR use the machanical shutter at 12fps and it's not an issue....OK...so that's a 12fps that's usable then...geeze...
While I appreciate the rolling shutter issue is a comparative ratio issue between the sensor read out speed and the object subects movement speed / frequency. The artifacts lead to rejected or unacceptable images. A stacked sensor design has proven to reduce the read out speeds significantly. The perfect solution is to employ a global shutter / sensor design...but I don't think Canon currently has access to the patent for this tech, they would have to develop a whole new aproach and patent that idea.
If an R5 has a readout speed of around 16m/s and the R3 has a readout speed of around 5m/s due to it's stacked sensor design, then it's plainly obvious that the R3 can shoot objects 3 tims higher speed / frequency rate without the rolling shutter artifacts being observable. Ergo...a photogtapher can actually use the 30-40 fps to capture fast moving objects and get usable (unrectable/unacceptable) images.