No doubt, 2nd hunters deer. It would be different if they were all trailing the deer and they jumped it and the other guy put the finishing shot on it. Based on what you said, that deer was no where near mortally wounded. We have had this exact scenario at our camp several times, although not at what I would consider a monster buck. It has always worked out for the hunter that deserved the deer.

If I were you I would do as you said, try and help him improve his shooting. Also I would send him the link to this thread and let him read what the overwhelming majority opinion is, as to whose deer it should be and why. Maybe he will understand, and let the rightful owner have the deer. Tell him to put himself in the other guys shoes....other guy barely wounds him and he puts the finishing shot on him a day later. Whose would he think it is then? Of course, some folks would think it was theirs either way. Good luck.