There is at least one scenario in which Tia may be correct: Xan was awful before. You made huge changes, and now Xan is amazing. Pointing out the strength of Xan at both points in time would not be a contradiction.
I have not looked at the stats. I do not know whether Tia's criticism is accurate or not. The above is a hypothetical.
However, regardless of whether that's the scenario we're in, you would be better off if you countered Tia's criticism by explaining how Xan was not awful before, or better yet, how Xan is not amazing now. That isn't (just) a moral argument. It's just pragmatism. While it may feel good to beat someone in argument by attacking them personally or denigrating their behaviour, that doesn't help improve your stats. And even if you feel your stats do not need improving, by leaving Tia's criticism without
real counter, you give people a reason to turn down your stats.
Apparently
this bcalc is the entirety of Tia's argument. If you truly believe Xan is not OP, you should be able to point out flaws. If you cannot do that, then I (playing the clueless newbie who doesn't really look at the stats, who just does what the big names say) have no choice but to believe Tia, even if he is literally 100% Hitler.