Theory of tubeless running lower pressure is that it doesnt have the tube in there to pinch flat, a dedicated UST tyre has a firmer carcass to it as well.
Check out the Shwalbe (spelling?) website it has a study on rolling resistance at lower pressures, it seems at some point the RR can reduce, running lower pressure and large volume tyres over something pumped up hard.
Yeah but there is less material not more in a tubeless setup – you would imagine having two layers of rubber would make the tubed setup stiffer.
Yes and no, the UST tyres are a bit heavier duty, take Spesh tyre or a conti supersonic & 100G tube and the tube type could have less rubber in it than a UST,, all depends on what your comparing as you have kind of hinted at in the OP.