You clearly instinctively feel that there is some relationship between an objective measure and a subjective appraisal of "all-around talent".. Indeed, there is, and that fact that you don't recognize that sales figures do provide that indicates, afaic, that you're ignoring some important variables. And note that, in this case, for the first time, you've switched from talking about vocal talent to "all-around talent" and in doing so I believe you've finally gone over off-the-rails with this line of reasoning: If you really are including talent of all types, then you have to factor in the talents for entertaining, for producing, for engineering, for marketing, etc. In that regard, i.e., with regard to what is truly "all-around talent", sales figures
do indicate who is and is not the best. (QED)
And of course in that regard music is a collaborative effort, with each person playing their proper role. As it has always been. The idea, that I think you may hold to, that music must be a solitary singular talent, has no basis in reality. While there are solo artists, of course, that is just one small facet of the discipline, not its entirety.
That's really the whole point.
What you're saying is that you personally prefer what they offer. The blurring of the lines between what is and is not your personal preference, and what is and is not "best", is dangerous. It is a very small leap from imposing one's own personal preferences regarding, say, entertainment, as the paragon of what is and is not best, "overall", and imposing one's own personal preferences regarding something more important, and
that is a pretty nasty societal problem.... but (paraphrasing Alton Brown: that's another thread).
The Grammy Awards is the industry honoring its own. They surely have the right to do so, but it is just an expression of some specific slice on a collective personal preference. I could get a bunch of software developers together and they could take a look at each others' code, and give out awards... but most reasonable people would project that what
really matters isn't what software developers think of each others' code but rather what customers think. While music is a bit different from software development, it isn't as different as you might think. The difference is evident in the fact that there are Grammy Awards, i.e., where internally-driven assessments (what the artists think of themselves) matters,
along with the assessment of society-as-a-whole (which brings us back to sales figures). Indeed, you can think of the Grammy's as solace given artists. However, it isn't the most important measure.
Indeed, the really important measure is something elusive in the present. We'll have to be long-dead before it will be apparent what is and is not really important
today.
Okay here are the promised pot-shots.
Celine Dion? Really. How banal (her music, not your liking her.

) Her music is excessive sentimental; going back to my culinary analogies, it's like a chef that uses too much basil. For me, she's the prototypical example of an instrument on legs.
(You get the idea.)