The battle of exegol is essentially a re-run of ROTJ where its palpatine trying to goad said subject to strike him down to fulfill his objective. While there are elements that are different than ROTJ (dyad, palpatine actually restoring himself etc). At this piont, its a matter of taste on how different it is to ROTJ and if there are any creative/meaningful ways to make the rey, ben, palpatine interaction more “original/novel” but thats a different discussion. I personally like what we got in episode 9 for what it was worth
Is it a rerun though? In RotJ it was Luke versus Vader with the Emperor watching. Him dying came as a surprise to him. In TRoS, Ben is already redeemed and both him and Rey have come with the explicit intention of killing him. It’s more like the LEGO SW level than the actual scene in RotJ.
If you guy really want the duel to take place during the battle, what if you just made Kef Bir and Exegol the same planet?
That would require a lot of work. Maybe make the Water somehow frozen, but it could work. If Kef Bur was maybe a different part of Exegol. It’s a weird concept, but would be cool.