In reply to irene46.

@IRENE46

The point is that I can mutate my vocal qualities COMPLETELY for different genres of music, some may like it more, some may like it less, but I can change my voice completely from genre to genre, while others simply sing the same way over different beats and call it "versatility".

Anyway, the "vocal expert" you mentioned does mention that Christina screams, does he not? And actually Phillipe Jaroussky (one of my favorite sopranists, by the way) read Christina's vocal flaws quite well.

So yes, some aspects of singing are subjective such as beauty of tone and emotion, while other things such as intonation, rhythm, resonance, vocal freedom, breathe support, etc are not subjective as they can be quantified, and those are things Christina fails at.
That's why you can argue that in YOUR opinion you like her because (again, things I mentioned) her tone and the emotion with which she sings, but when it comes to TECHNICAL aspects of singing, her flaws are evident.