I don't really feel its his weight that's the problem. His lack of flexibility is probably more of an issue.
I am sorry but that is truly the most disgusting disregard for a horse i have seen in a long time. To me it's not funny, or entertaining, it is blatant cruelty to animals and i feel there is a massive need for education in horse welfare in the community in which that was filmed!
I don't really feel its his weight that's the problem. His lack of flexibility is probably more of an issue.