You are correct it is part of warband itself and would be nearly impossible to change. The amount of time it would take to rewire the entirety of warband to allow the models you see be the hitboxes would be a lot more work than it would be worth. A good example of how much work it would take is CS:GO. It took Valve 3 years to go from blocky hitboxes to these new fancy hitboxes here:
So to put it all into perspective it took a major game production company
3 years to change a system in a game
they created. All we have is a few dudes who develop out of the kindness of their hearts (I think...). Sorry if I burst your bubble but I figure this thread needed a decent explanation. If you were just a person posting a photo in the forum to have a giggle then "cheers m8".