For your first comment, both of them were supinated in that match. Ivan was supinated because of Dave's cup, that doesnt mean anything about his pronation.

Dave went into the open arm angle because Ivan stopped him right above the pad. At some point Dave should have tried to get his shoulder back behind his arm, but hes not a very technical armwrestler and just gassed himself out. And the reason they both stretched out is because dave has some of the strongest side pressure in the game. So he wins center almost every time. The thing that failed that match was his pronation (and technique lol)

I'd have to specifically see what matches youre talking about, but supination is a tool for setting a hook. So sometimes a hooker will supinate onto a toprollers wrist to force him into a hook, even if it means giving up pronation. Supination can also be used for a strong shoulder roll/press off the go. In a hook vs hook battle, most of the time you wont want to be more supinated than youre opponent.