Guys who don't have good chins usually have that body type : lanky with a thin elongated skull (Sillakh latest example). Williams is an exception, that shot by Martinez would have knocked out most fighters.
They need him to gain some weight.Period. Being 220 and 6'7 is ridiculous. Hes the same weight as a prime Tyson and 8 inches taller. Hes the same height as Vitali and about 30lbs lighter.
Actually you can. Strong neck and leg muscles plus bent knees can absorb a good punch. I know because i was rocked bad in my first fight by soft punches. Now i train my neck everyday and it (my head) doesn't hurt when i get punched. But it´s not like you can go from glass to iron. If he really has glass then he will get stretched bad one day