He's so damn attractive - and so unsurpassable on that track with Basie.
Maybe he was just too good a singer with not enough dirty bluesiness in his voice for the Stax and Motown stuff. He sings really well, but that's not his genre.
That's simply what it is. I have that CD. I only new his 1940's stuff before that, but once I got over the superficial aspects, my admiration grew.