This seems counterintuitive, but let's consider Zhongli's narration. We can definitively say that Xiao is remembered through music- the medium Venti uses to honor great heroes. Regardless of his feelings for Xiao, he believes he has to use music to honor him. As an Archon, he seems half-invested.
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After all, he decides which roles he cares about filling; this ties into his belief in freedom. Consequently, he freely chooses to remember Xiao, even
Xiao is calmed by the song obviously, but he also honors devotion.
Xiao realizes Barbatos (and he knows it's Barbatos there's evidence of that) can actually be devoted and caring. He sees another side to him too.
Imagine Xiao coming back, recognizing who he is (both human and god), and unexpectedly thanking him for a performance. That his devotion +
There are few people, if any, who understand all of who Venti is. I think that if Xiao showed up and acknowledged his value, it would probably have a similar effect to the impromptu performance.