Yes, we are with little hints from the nebulous statements in the OMs like Toyota has saying use a higher viscosity for more extreme use conditions.All fair points. I don’t disagree with the science. I believe it. I have used a higher viscosity in several vehicles when racing, towing and off roading because it was absolutely required.
The hard part to define with this particular topic is at what point is it actually impactful with “normal” or “extended” use. And this gray area is the hard part. And manufacturers won’t clearly define that break-over point for us. So we are all left to decide for ourselves.
The easiest way to take care of the unknown protection break point as you call it, is to establish the protection headroom right off the bat. Only thing that might be a negative from doing that is loosing a tiny bit of fuel mileage.
Example: Go up a grade if xW-16 or xW-20 are speced for "normal" street driving. If xW-30 is already speced, go to xW-40 or xW-50 for really heavy track use. Ford specs anything from 5W-20 to 5W-50 in the high HP Coyote V8 based on use conditions. Most high performance car makers run a thicker oil, and spec thicker for track use for a reason. Thinner oils don't protect as well in those situations. And some like Ford have went back up a grade (5W-30 in the Coyote now) for normal street driving. They wouldn't burn their CAFE cash if there wasn't a good reason to do so.