Is the 338WM too much for deer? I say no. Not if the guy has no problem totn it around, hits where he aims and MOST importantly HE LIKES IT. Who cares what he hunts with as long as it's legal?
My daughter dated a guy that did all of his hunting with a 375 H&H. That means pigs, deer, bear, and he hoped Africa some day. He sure knows where to aim.
A hunting buddy of mine uses his 300 WM for all his hunts. Not many use a 300WM with 180gr bullets for antelope, but he does. Same load, same bullet for everything. It works, and I lost a $5 bet to him one morning that he couldn't hit a 12" rock that was nearly 400yds away. He sat down, braced the rifle on his knees, and the rest of us watched the rock powder fly. this guy knows that big gun.