Exactly right. The wrist shouldn't be jamming and with the better grip pronation /forearm rotation wouldn't be obstructedAt contact, the wrist should be in a roughly neutral position. Or perhaps slightly extended. But wrist should not be beyond neutral at contact.
It appears that Nishikori overly flexes his wrist beyond neutral. And does not properly employ pronation and Internal Shoulder Rotation.
As for the grip, I think you are saying Nishikori was not using a Pro Grip and that led to the wrist issues.