Yeah I've seen a good case or two that he didn't want George a second time. Holmes didn't rematch any of his close opponents, Weaver, Witherspoon, Williams. Ali certainly beat Foreman more conclusively than those threee were beat.
This is not close enough where this amendment matters. Alis still got Holmes in terms of both quantity and quality.
I think Ali was done with difficult challengers after Norton 3 if the money wasn't something special. He said himself that Shavers was a cherry pick gone wrong.
Could another fight with Foreman have realistically happened again? Ali was busy in 1975 and 1976 and then Foreman lost to Young in 1977. I think Foreman want a rematch though.