I can’t help but think that the natural climax of TROS would’ve been the Kylo Ren and Rey duel, where Rey almost kills, then chooses to heal, her mortal enemy.

I take it you’re referring to the Death Star ruins duel? It’s an important scene, yes, but it doesn’t wrap up the story. You need Exegol for that. And if we’re going for parallels, RotJ didn’t just end when Vader killed Palpatine, they still had to blow up the Death Star. Is it as emotionally impactful? No, but it’s still a necessary resolution. The same goes for Exegol. The way I see it, the trilogy’s arc of Rey and Kylo wraps up when Kylo throws away the saber and Exegol is a sort of victory lap.