In Japan, the WRX S4 is only available with the CVT, no manuals were available. The CVT S4 make a lot more torque than the WRX manual. So I think the weak link is manual (NON-STI manual that is).
Regarding how the CVT behaves when being flooring, I observed this behavior in all Subaru automatics. The 4EAT in my old 98 Legacy GT, 5EAT in my Tribeca, 05 Legacy GT, Legacy 3.6R, and now my Ascent and 2020 Legacy XT don't like to be floored. However, similar to what you observed on the highway, if you just press down on the accelerator without stomping from a stop, the Subarus will accelerate hard. It is just Subaru being weird.