Both in their prime, under UFC and Pride rules who wins? This is a fight I've always felt Mirko would of won if both at their best. I believe Mirko could do what Shane Del Rosario did to Stipe but even better, also if Daniel Cormier could walk in straight lines with his hands down at Stipe then Cro Cop would definitely get major success seeing as he's a much better striker with use of angles and kicks. Stipe could possibly takedown Cro Cop but at the same time Cro Cop had incredible movement and sprawling ability to get away from the takedowns. I'd go with Cro Cop by stoppage.
I always felt Stipe was basically a very good HW who found himself in the right place at the right time to catch a bunch of big names as they were in the twilight of their careers, and that lead to him being overhyped (mostly by the UFC but to some extent by fans too) as GOAT HW etc etc. He was obviously well rounded, tough and durable but I dont think he would have been anywhere near as accomplished in stronger eras. As for Stipe/Cro Cop, I think Mirko KOs him under Pride rules. Under UFC rules i'd give Stipe the edge as I think he'd have more success with his wrestling, Cro Cop and cages just didnt seem to mix well.
I have a hard time seeing Stipe be able to stand in front of Mirko and trade to be honest but I respect your opinion.
Stipe is definitely one of the best heavyweights ever just for the success he had in UFC with his title run (I have him at 2-3) But from a H2H standpoint I think Fedor, Cro Cop and possibly Velasquez could of beaten him. He traded wins with Ngannou but I think Ngannou will surpass him.