Well the only guys I think would ko frazier are foreman, tyson and louis, so take your pick. As for could, holmes, lewis, wlad and bowe have a shot of blinding him with jabs and kicking his arse with power shots late on.
Ali was punching very hard in Manilla. He was trying to put Joe out early and humiliate him. That was the most vicious I ever saw him punch in his entire career. He was planting his feet and putting 225lbs into those shots. Not many heavies survive those punches in Manilla. Like almost nobody.
There is no weak puncher who could KO Joe Frazier. It took Foreman six knockdowns before Mercante stopped the fight against an unmotivated, overweight Frazier. The only way a weak puncher stops Frazier is by virtue of the ref stopping the fight.
Oscar had him hurt in one round out of twenty five ... in addition Frazier was extremely green at the time ... Quarry never seriously hurt him ... when you factor in he fought almost his entire career blind in one eye and combine it with his style his chin was pretty amazing to me ...
People thinking "weak" punchers can't be effective ones Please see Frazier never hurting Bonavena but Folley and Ellis knocking him down.
So it's agreed that even a past prime Joe Frazier had one hell of a chin...or maybe Ali was just a weak as hell puncher considering the bad intentions you describe him as having vs Frazier in that 3rd fight.
There isn't one on the Planet Earth,,,,,,,,,,, Nobody could 'Knock-Out' Smokin Joe Frazier,,,,,,,, let alone the 'Weakest Puncher' A KO is 'the condition of being knocked-out' Boxing term; 'unconscious, or on the canvas for a minimum count of 10-seconds and unable to rise'
Hence this thread should be retitled, "Weakest puncher who could KILL Frazier?," because that's likely what would be required.