Theres certain things dominant champions have in common and one of them is a good chin. Look at how often Lee gets rocked - when has something like this ever happened to Bones/Holloway/Khabib/Mcgregor? It is ESSENTIAL as it is the difference between an 11 title defense streak and getting knocked out on the first. Also a lot of chinnyness comes down to how you hold your hands, head, roll with punches etc. and Lee just isn't there.