4 heavyweights with 3 things in common, I'll give you 1, which will leave 2.

[beenKOed]

I'd guess one being that none of them ever got a chance to fight for a proper HW title, they were avoided by the likes of Dempsey or whichever other white champions? No clue as to another.

This and the fact that they fought each other multiple times, Oh and beenkoed Langford was Canadian eh

If you say he was Canadian, he was Canadian!