All your logic is sound and you may be proven correct. Except also, as you put it, nothing is set in stone. I still think Pogacar is an equal talent and assuming he will decline at a younger age is speculation lacking evidence. There are two reasons Pog lost last year’s Tour. One of those reasons can’t be discussed here.I guess Extinction's reasoning is that 2 years ago, Evenepoel was walking on crutches, while Pogacar was being heralded as the "true" new Merckx. Since then Pogacar has hit his limits and not really progressed and got a big dent in his shining armor, while Evenepoel, after 9 months of recovery and an extra season to get back on track, has since made huge strides, now being one of three riders in history to win a monument, GT and WCC in one season. It's reasonable to assume Pogacar has indeed hit his limit or at least a point where any progression will be marginal, while we don't know about Evenepoel since he's still on an upward trajectory.
Doesn't mean anything is set in stone. For all we know Pogacar will drop the "vroom vroom" racing and turn into a cynical rider, wasting no energy and taking a more clinical approach to boost his efficiency even further. Maybe Evenepoel doesn't have any headroom either and we'll find out in a few months. But i guess at least the assumption that Pogacar is no longer on an upward trajectory, doesn't seem completely unreasonable. If Pogacar on the other hand had the same bad luck Evenepoel had two years ago, or that of Bernal on multiple occasions, he could also find the best part of his career behind him.