Don't confuse strength with flexibility. Strength is the amount of force required to break something which, in this case, means deforming it so it doesn't spring back to the original shape. Flexibility is the measure of how far it deflects under a given amount of force as long as that force is less than the breaking force. These measurements are totally different.

So thin-walled hi-ten might be vulnerable to breaking, but until it breaks, I expect it to behave and feel like thin-wall higher-ten, to coin a term.

I do get that, I think. I was just thinking that it must be possible to design for a certain amount of flexibility, given the constraints of the material's strength. But although I loved science courses in college, i never did anything in the fields of engineering or material sciences.

Yes, I'm sure bike makers design a bit of flex into forks. To get extra flexibility, they use thinner walls or perhaps smaller diameters. And to do that, they'll need a stronger alloy. So it's a tradeoff between flexibility and cost. They have to meet a minimum strength standard, and I gather the regulations require higher strength than before. I'm under the impression that current-production steel forks are heavier than they were back in the day. I've kept bike shops in business since 1975, not long before you.