....these points lead me to believe that this uoa is relatively worthless when held up against other uoas from vehicles with stock oil capacities....
You make a point if you are strictly comparing the volume of wear metals in different vehicles. But it's definitely not "worthless" comparing how the oil is holding up in the engine for long OCIs.
There was a thread years ago on JeepsUnlimited.com by a guy that compared various filters in an elaborate experiment, and sent the oil to several places for analysis. He then popped on a bypass filter to his setup without changing the oil, ran it a relatively short time and sent another sample.
The results? The oil from the bypass filter test was much cleaner than all of the other tests. That meant that many particulates, including iron were getting trapped in the bypass filter. It also significantly reduced silicon levels.
That convinced me that the ppm of iron on the UOA is less than the total ppm of iron generated over the OCI. You can't really measure wear through a UOA when using a bypass. Furthermore, the F20C engine in the S2000 has FRM cylinders, not cast iron and the block & head are aluminum, not cast iron. The prelube pump helps too. The true proof will come when I see how many miles I put on this engine.