Thoughtful posts. If you're not into jazz, I can see why you wouldn't like this. I like all vocalists mentioned, including Diana Krall. Ella had just divorced Ray Brown when I was in California and helped me with chord inversions.
She isn't a commercial talent at all, but if you check out her credentials, you will find that she is a world-recognized talent.
Responses have been personal preferences, and that's the way it should be. Jazz elitism will NOT raise it's nasty little head here.
Just check her out and look at her world-wide accolades.
She is one of my top two female vocalists of all time.
And this performance with George, Toots, Quincy and Rochelle really is why I do what I do.
It may also be why I make most of my money playing for a recording machine and not live audiences....YA THINK? (LOL).
Be well, all.
Russ
P.S.
There are other niche performers. Check out Leanne La Havas. Much more commercial appeal, but not for everyone.