I don't know that Foreman had the "style" to beat Frazier, maybe it had a lot to do with when they fought. Frazier was a small, pressure fighter who had to be motivated and in excellent condition to beat bigger, stronger fighters. For the Foreman fight he was not motivated according to most, in fact, from what I have read, he spent more time playing with his band than training, and he was not in the same condition as he was in 1971 and before. Frazer had not looked impressive against Daniels or Stander who were not considered competitive and he was not in great shape or motivated for Foreman either. I don't know if the JF of the Jimmy Ellis or Ali fight would have beaten Foreman, but I wouldn't bet against it. Frazier, at his best was quick, had a good defense, and good stamina in addition to a good offense.
Joe Frazier had a very good chin .. keep in mind he was a small swarmer fighting his career at heavyweight and was partially blind in one eye through out almost all of his career and look what he accomplished ... the only stoppage ( not blind in Manila) at the hands of murderous punching Foreman and even George couldn't keep him down for the count .. His chin was an A .. not the A plus of a Chuvalo, Mercer or McCall but still terrific ..
While I do believe your point about Frazier not being at his best when he fought Foreman, a good point I'll add, he fought a larger man in Buster Mathis Sr. That "Small" Heavyweight Frazier didn't have much of a problem with Mathis whom was the same height as Foreman but would've been heavier than him by a little over 20lbs. Its what Foreman did and how he fought was the major difference. Foreman's incredible physical strength and how he used it to his advantage was a major factor in his win over Frazier. A physicality that was uniquely his own. Their have been taller heavier Heavyweights than Foreman, but none used the type of physicality he fought with.
It was Frazier's immense heart, his raw courage that kept him in hard fights, not an exceptional chin.
I do think that it had to do with Joe Frazier taking the punishment that he took from Muhammad Ali, physically and emotionally on March 8 1971, that Joe began to decline, and led to his knockout loss to George Foreman on January 22 1973. In the interim, Frazier faced the likes of Terry Daniels and Ron Stander. And remember Frazier took the heckling of Ali during his 43 month banishment from boxing, 1967-1970. Ali was considered as the champion as he never lost the title in the ring. Joe had a lot to deal with.
He had a mid chin, kinda like lennox lewis. he got dropped early in his career by no name mike bruce and in the 1st bonavena fight he got dropped twice in the 2nd round n a fight with the 3 knockdown rule. obviously george foreman hit like a tank so i wont hold that against joe. the other knockdowns though.....? idk