The purpose of motion blur is to fill in the gaps between frames, adding information on the speed each object had. This mirrors the behaviour of film, but it can also look good in games (it creates the perception of continuity).
There's no perfect solution, but given gaming is moving beyond 30/60FPS, we shall also update our engines to reflect that, and make sure our games will feel good on future hardware.
However, for that to work as intended, the shutter speed needs to be based on the current frame's length
UE doesnt adhere to this principle, instead going for a fixed 30FPS length
At high FPS games feel more blurry than they should, given that blur travels faster than the camera, with jittery motion
Would you like me to keep posting here?
I'd love to, but it takes me time and only the usual 3 people see it. Not sure it's worth it.
Regarding cutscenes, there's nothing to worry about.
Devs can still force motion blur to 30fps, or 24fps, to have a more "filmic" look.
This is yet another controversial post processing topic, which is ultimately down to artistic choices.