He was tagged on the chin good several times in his career, he always showed a good chin. He just killed himself with the weight drain and age caught up with him.

Look at the case of Chris Byrd: he fought at HW his whole career, took bombs from David Tua, Holyfield, both Klitschkos, DaVaryll Williamson, Golota, and a bunch of other HW bombers and was only stopped a few times. At 38, he decided to cut down to 175 and fought a guy who couldn't punch at 175, and he literally got hurt every time the guy layed a glove on him. He had absolutely no punch resistance.