The supporting evidence you present are correct, but I'm not sure if I agree with your conclusion. What you're describing is technique, not artistry. One singer--or skater--could very well have better technique than another, but not be as good artistically. It's true, however, that good technique can help a singer/skater better express their artistry (e.g. someone with good jumping technique can probably land their jumps more often, and avoid having falls wreck their skate).
I agree with you that Christina doesn't really have much of a high register. And her technical abilities are overpraised. But--I think she's hailed the way she is precisely because of her growls/screams. Her voice--love it or hate it--is powerful and distinct. Beyonce may very well be a better technical singer, but I can imagine others singing her songs and doing a credible job. However, I don't think anyone can sing Christina's "Fighter" nearly as well as the original.
(For the record, neither of them are my favourite or least favourite singers. I just see merit in both: Christina's edge being her voice itself (skating equivalent = charisma, performance ability), whereas Beyonce is more about how she uses her instrument (skating equivalent = technique or choreography). Is one artistry, and the other not? YMMV, but for me, both can be artistic.)
Christina is like Yulia for me, not artistic, not particularly good on the technique (although for Yulia it's only her jump technique that is questionable), packages stuff well and presents a wow factor well (growling a lot, lots of runs and riffs, screams). It's not particularly artistic while the way Beyonce chooses to embellish her own performances and interpret her own music differently every time works. Christina's sound is distinct and she's a charismatic performer but that's all I'm going to give her. I don't think she's artistic.