I actually don’t think either guy has a bad chin. I just think AJ gets way too much criticism. How can a chin be that bad if it’s been consistently holding up at an elite level. He’s only been stopped once at it took a complete beat down to do it, and he was still on his feet
Wlad is as big a puncher as anyone in the heavyweight division, possibly ever. AJ shipped a perfect right hand and got up to win the fight. His chin is really OK, his recovery powers at world level are poor. Wlad himself was too tired/affected by the punches he had taken from Joshua to take advantage. Or possibly he could have but big brother advised caution.
CHIN = JAW resistance + RECOVERY (reaction to shots) ...therefore... If it's true that AJ's jaw is good not the same can be said about his recoveries if hit hard so his chin Is to be considered at least: SUSPECT.
If any HW is hit hard they are in trouble, Joshua is no different. It’s not like he’s getting rocked by jabs and grazing shots. The times he has been rocked they have been big shots. His recovery is weak in the sense he is isn’t great at tying his opponent up or clinching to buy time and stop an onslaught. For example, Fury is great at this. KD in round 7 of the first Wilder fight springs to mind.