You're making it too hard, JJ
Jungle Jim: Strapping is already optimized for tensile strength in the direction of the load. The warp threads are strong, and the weft just stabilizes. Polyester is just so strong, with strength, holding layout constant, roughly proportional to weight. How strong is that? About 1/3rd the strength of Dyneema cord of the same weight.
So, your optimization will be from not having straps that are too long or too strong. Some folks already use composite straps to reduce weight and bulk, part of the strap consisting of Dyneema cord which will not come in contact with the tree. Well, not until you come on the unexpected situation that there are no trees to hang from smaller than 3' / 1M diameter ones, and your straps, composite or not, are just 6' / 2M long. In that situation you set up with a dummy load in the hmmk, and place found lots of found sticks under the the portions of cord in contact with the sides of the tree(s).
Hip, hip, hooray for three mules
Or two or three strips of 3/4" mule tape in parallel. That's the stuff that is likely ideal, once it is cleaned of lubricant.
If I thought there was sufficient demand for Dyneema (tm) tree straps, I'd have commissioned them for production and resale. And, so, too would several other regular dealers before me who likely looked into it. <smile>
So, at a weight penalty of twice Dyneema's weight, mule tape, thin and optimized for tensile strength, may be the best thing.