Wallmonger

They live close to you? If yes maybe you can go to their house and test it yourself. Some people is not sensitive to input lag while some does, maybe your friends is the former.

It is a weird one.  That particular issue is generally specifically mouse related. 
 
let’s look at the mouse input signal:
signal goes through usb to computer and is interpreted by the mouse driver (mouse driver issue?) 
it goes from the mouse driver though windows to the game (windows settings issue?)
it goes to the game software that implements it. (Specific game issue?)
 
if it’s supposed to go through the driver directly to the game skipping windows and isn’t for some reason windows itself could be the delay (bios setting issue?)

Is your mouse wireless/have you tried a different mouse? Storage shouldn't be the cause of mouse input delay. The other thing I can think of would be your internet connection if you are playing online.

What mouse?  Every spec was mentioned but mouse model doesn’t seem to have been and you’re talking about a mouse problem.
 
is it perhaps a wireless mouse?