I gather you have tried it yourself and agree there is an issue?
The slide on the 4056TSW should not be significantly harder to retract than on any other 3rd gen S&W. The short .40 guns usually have a dual spring and a fairly strong spring, but nothing that should be that noticeable to most shooters. I have not shot an M&P, so I cannot compare the two.
I would wonder if a prior owner went overboard with an extra power recoil spring or if there is a lube/galling problem. Does the gun function properly?
Worst case would be something wrong with the slide or frame or the fit of those two. Unless you are are quite confident of your ability to take the gun down and look for issues, call S&W and they will send a fedex label. Send the gun to them and they will put it right or tell you it is in spec.
If there is nothing wrong with the gun, consider helping your friend find another gun that may be better suited to him.