CYe Yes, he had the better chin. He was never stopped by one punch like a certain other heavyweight (twice). Even a shot Bowe took tons of shots against a pretty decent puncher (Golotta). You can argue Lewis had more power, better defense, better ring generalship, better overall competition, but not better chin. Can't believe you're using sparring where's the proof that even happened) as evidence of a weak chin.
I watched the Biggs fight earlier today and Bowe was clearly hurt a lot by a modest puncher in Biggs on more than one occasion, especially at the end of the third when he had Bowe staggering into the ropes. Bowe's punch resistance does get over stated as he didn't face many punchers, he had a ton of heart but his chin wasn't iron. Holyfield hurt him and even dropped him in the 3rd fight, Hide had him hurt a number of times and of course Golota had him out on his feet on more than one occasion.
Mercer is like Witherspoon in that he seemed out of shape too often in what should have been his prime and then tried to play catch up later in his career when he began to get long in the tooth .. Ray just seemed dangerous but often off a bit .. Bowe was bigger and far more talented .. I see Bowe winning a decision .. however f it becomes a slugfest who knows ..