I know I've explained this before, but I'm OK with the concept of a company taking an approved additive package (which both HPL and AMSOIL do) and then using that with a superior base oil blend and performing some (expensive) top treatment to improve certain aspects of the product.
Fundamentally, the AW chemistry present did indeed go through the testing in question, and there is direct and considerable knowledge of the constituents and base oils, and there is testing involved, so it's not similar to just using an additive to increase the quantity of a certain component.
As you know, I'm a big fan of the A3/B4 LL-01, A40, 229.5, 502/505...etc additive package and oils like M1 FS 0W-40 that carry those approvals. It's a robust suite of approvals from a variety of euro manufacturers with a focus solely on performance, since there aren't any limits on phosphorous or other constituents. Personally, I'm quite comfortable with that same additive package being blended with PAO, AN's and esters, with some additional attention given to FM performance (not part of the approvals) by one of the foremost authorities on tribology and who was behind the development of that very base oil blend. Others may not be, and there is absolutely nothing wrong with that.
But, I think it's important to note that the approach HPL has taken here is quite different from that of Redline for example, who, historically, used what appeared to be the same additive package in all the white bottle oils (Euro, PCMO, HDEO...etc), which was a racing-style chemistry with no approvals out the gate. That doesn't make it a bad product, but it does make their approach considerably different.
AMSOIL produces many actual approved products, and their approach to chemistry in their SS lineup is much more like HPL's. They've embraced Group III and GTL in their premium products however, without coming right out and saying it (and, even per Dave, Group III is not a bad choice and may even be advantageous to blend with vs PAO in some respects, depending on the grade), while HPL is very transparent on their base oil blend composition for their different product lines.
I also appreciate the lack of outrageous claims. No "this oil contains friction eliminator 9000! this isn't your grandma's chemistry, we don't just reduce wear, we ELIMINATE IT! We free those horses, STUD HORSES! SO MANY HORSES!!! BRAHHHHHHHH!!!!"