What makes you think Foreman would knock Ali out? The next defensive fighter he faced beat him on points and dropped him.
Frazier and Ali should have rematched, without being allowed to clinch excessively Ali never beats Frazier. That fight have the blueprint for Wlad to dominate for a decade. How to neutralise the perfect inside fighter. Ali also should have rematched Foreman but Foreman couldn't get past Young and then retired, before returning to prove boxing didn't advance over the next 20 years. Either way neither are ducks. Frazier and Ali fought a trilogy so no duck there. Ali knocked Foreman out so no duck there.
You can hardly say he clinched excessively in Manilla. You must be thinking of the second in fight. In Manilla Padilla slapped his hand down every time he tried to hold. He was more past his prime and he beat Frazier. Nothing more to prove there.
Ali was prevented from excessive clinching by the ref in fight 3 who constantly pulled Ali's glove off the back of Fraziers neck. So Ali indeed best Frazier in fight 3 without excessive clinching. He beat Joe in many ways at his own game that night.
Ali owned Foreman in that fight, as far as George was concerned he couldn't hurt Ali, that's gotta mess him up. why would Ali duck that?