The Machen fight tells us a lot. Ingo had the kind of power/delivery, where a superior chin, didn't promise you anything! He was very beatable, but also very dangerous!
Imagine if Ingo was forced to make a mandatory defense against Sonny Liston in 1959 immediately following his title winning knockout win over Floyd Patterson also in 1959.
I think the best one of the lot he’d have a shot to smite is AJ. Holmes and Ali are just too sturdy. I don’t think he does cut Joshua down but it’s “possible”