The Ironman vs Thor fight made it clear that Stark never had a chance when Thor started crushing the armor with his bare hands after taking Starks best shots. If you meant Hulk vs Ironman, it's not hard to believe that working along side Banner studying all aspects of the Hulk that the two of them would be able to come up with a weapon to contain him with a large amount of effort.To be fair, DC is kinda on some dumb shyt, I mean no one else is putting dumb shyt in their movie like a rich billionaire playboy going toe to toe with a god in a special suit they created.
The issue is that there are people would argue that a super fast, planet busting, flying talented fighter like Goku would have no chance against Superman but some of those same people look at Batman vs Superman as a valid fight. That makes no sense.