According to Pep, chins don't get better with age

This is correct. Thankfully he didn't mention Jimmy Young. Foreman was up at 10.1s at worst vs Ali and fully coherent to say the least. He'd simply punched himself out. You are correct to say he took loads of Ali's best punches with ease too. Frazier's best left hook was like, is that it? I only recall seeing him genuinely scrambled against Lyle. Lyle was obviously a big puncher and you'd have to think hit way harder with single punches than the likes of Frazier who had very good power as it was.

 

Totally. Toney got hurt and buzzed substantially at 160 but took some big punches way north of that. There's a chance his weight draining may have contributed as well tho to bring in another factor. It's still hard to see 160 pound Toney taking some of the blows he took at 175 and upward however.

 

There's a bit of a disconnect on Ali. There's a strong theory his chin suddenly got better after exile. Banks and Jones and Cooper are brought up as evidence. Against Banks Ali was 20 and sub 195 pounds in his 11th bout. He was 21yo and 202 pounds against Jones. Cooper was right after and Ali is now 207 and still 21. Cooper has one helluva hook tho and as Romero hinted, sometimes it just happens. Griffith was sparked against Carter, Kalambay vs Nunn, Lockridge vs Laporte etc etc ad infinitum. Holmes dropped like a lead weight against Snipes and fell face first into the turnbuckle rising. It happens.

Next up is Liston, he's 22 now and comes in at 210 tho he did come in at 206 in the rematch. Ali soaked up some bombs off Liston including when he was blinded. Was Ali ever even stunned again pre-exile? One can berate his opposition but wait, he took some bombs off Liston who is one of the greatest punchers ever. So from Liston to exile, a 3 year period, he was in no trouble whatsoever.

By exile Ali was coming in at about 212 1/2 and it's safe to say at 25 he was well and truly developed physically and at the peak of his powers given he didn't fight again for years. If he wasn't at his peak for durability he was damn close to it. Just because he didn't have to prove it doesn't remotely mean it wasn't there. He proved he could take a bomb years earlier vs Liston. Sure he wasn't beat on for round after round but a guy like Liston didn't have to beat on people continually to get noticeable results.

 

I think In the vast majority of cases that assertion is correct.