I think Stipe's prime started a couple years after that and it was a very close fight, I remember thinking that he may have won at the time. He was definitely an up and comer to watch
So Stipe himself was already 32 in that fight. I agree he wasn't in his MMA prime yet but his improvement in skills has to be balanced against the fact that he himself was no longer in his athletic prime. And everyone else was a carcass compared to him.
Basically it was an old man division, where Stipe was always younger than his opponent (except green Francis and post Cain-JDS), with much less miles on him. He is an enigma because of his own late start in MMA.
Absolutely nobody he beat after that first JDS fight was in their prime.
Hunt - 41
Arlovski - one month from 37, 17 years in, 8 times KOd
Werdum - one month from 39
Overeem - 36, 17 years in, 13 times KOd (in both MMA + K1)
JDS - Younger than Stipe. But no serious MMA fans thinks JDS was the same fighter after Cain 1 + 2, Overeem KO and Stipe 1 war. There's a reason JDS opened as a massive betting favorite in first Stipe fight yet a significant underdog in the 2nd despite winning the first time.
Ngannou - As discussed. You can argue the 2nd Stipe fight was as much Stipe out of his prime as Ngannou was green in the first fight. But the fact Stipe got destroyed by a non-green Frank doesn't give him much credit for the first fight.
Cormier - 40/41 (39 when Cormier beat him)
Stipe's entire UFC record vs people younger than him is 4-3. His record against people older than him is 10-0.
His legacy is a Turok lie.