I get what you're saying about different types of performers, and I completely agree, James Brown is no less of an artist than Eric Clapton just because he didn't sit at a stool and play an instrument. I also agree with you that their is a heavy bias towards these artists and it most likely stems from the culture of racism in the music industry. Throughout history and right up until this day, black artists have never been afforded the same exposure or respect as their white contemporaries and the history books have (successfully to some degree) done everything they can to gloss over the influence and impact of so many black luminaries. They never get celebrated in the same way compared to the likes of Elvis, Dylan, Springsteen and the usual suspects. I'm sure you already know that, so I don't need to go into it.
Having said that, I think the desire to see Michael strip things back isn't anything to do with trying to get him to fit into the mould set by white rock guitarists (seemingly the only type of people who can be taken seriously by these elitist magazines and critics). I think it's because, unlike Clapton or Springsteen or Dylan, MJ could've done both. He was an amazing dancer and showman and yes, that is where his roots lied, inspired by the likes of James Brown and Jackie Wilson etc. But he also had a remarkable singing voice which so often gets overshadowed by the MJ package of bells and whistles. If he had of done an MTV Unplugged, and sang completely live for an hour and a half, doing acoustic versions of One Day In Your Life, She's Out Of My Life, Who Is It, Billie Jean etc, it would've blew all the other try-hards out of the water. Forget Nirvana, forget Clapton... MJ would've owned it. It just frustrates me, as a fan, that he is not recognised or given credit for being an amazing singer, beatboxer, songwriter and musician.