I tell you one heavyweight who was fackin awesome in the clinch and is now a boxer....matt skelton!! Remember the k1 uk he won, he just clinched every fight. So strong and so good with his knees. You would never guess he would go on to become a boxer. Bonjasky was another one, but yeah your right most heavyweights are crap in the clinch.
I was at that event in Brum & am a fan of Matt's. But come on Donnie mate u know as well as I do his level of clinching is galaxies apart from even the most basic level of the lower divisions in Thailand.
Most of that is due to many of the techniques not really being practical for a 230 guy to do though. It's different moving a big guy and its harder to move as a big guy. I don't think it's as much a lack of skill as much as just physics, I bet a lot of the elite heavyweight strikers could teach and know a lot of the little guy techniques in the clinch with spinning and trips etc, its just too hard for them to do often in competition. I'm no thai expert but it happens the same in grappling. As a heavyweight wrestler myself I don't use many of the techniques that say a 125 pound guy will use such as funk rolling as its not practical doing to another heavyweight, but I could teach these techniques to someone nonetheless and know what they are.
U font have anything like that in Thailand, u don't even need a licence to fight u just need to show up with your nut guard and gum shield.