Let's assume that this is speed equalized since if not then Dantes blitzes to hell and back
R1: They both pretty much resist each other's hax. Dantes is starting out with about a x2 AP advantage, but Xiao can match that with Bane of All Evil plus massive multiplier scaing on most of his moves. He counters Dantes's Reactive Evolution with his own via Dissolution Eon - Heaven's Fall, plus his durability doubles when under half health. Attendre, Espérer: Wait, and Hope is countered by Xiao's own healing and phys vamp. I'm honestly leaning towards Incon here. Neither of them can put each other down for good
R2: Assuming Ritsuka is Dantes's master, Dantes loses since he can't keep Xiao away from Ritsuka forever. Xiao's going to realize that Ritsuka can back Dante up, and he'll hyper focus on her as much as possible. This, along with his massive AOE, will allow him to pick off Ritsuka sooner or later. Since Dantes can't resurrect the dead, once Ritsuka's dead he can't maintain his Spirit Origin anymore. Xiao should win
R3: if Traveler dies, which they most certainly will due to paltry 7B dura and lack of utility, Xiao's gonna get pissed, and try to end Dantes as soon as possible. However, the stalemate from Round 1 still apply. Incon
R4: Same as Round 1. Incon
Overall, Xiao should win by a slight margine, assuming Dantes's hax aren't layered.
If Dantes's hax are layered, then he auto wins due to soul hax and corruption, but if it's not, then Xiao resists it all and stalemates him.