Like it or not, weight matters. People can argue all the want about being balanced, or not, bottom line is someone that is heavy is hard on furniture, toilets, floors, beds, so why would it be okay on a living creature?
I have to ask as politely as possible what is your beef with us fat people?
I totally respect your views on larger people riding, and yes at 30% caution should be used.
What gets me is you constant assertion, every time this is mentioned, about the affect of heavy people being hard on furniture toilets and beds, I mean get real.
OK, stopping there because I cannot phrase what I want to say in any polite manner at all. If you have such a thing about large people you had best stay away from us, we may fall on you and squash you.
I really don't know if your horse would be OK or not, the thing to do is ask him, as in try it and see. It sounds way at the top end of what he should be carrying, and I'm sure you don't want to damage him, so take it easy, and if your horse shows any distress then you need to speak for him.