I know slut-dress when I see it. She can't depend on her voice, so she tarts up big time (if you think that her pants down to her pubis isn't tarting then I assume you are Gen-Xer).
She waters down her singing by slutting up (or down). As I said, sad. As I didn't say: unnecessary.
As the saying goes, beauty is in the eye of the beholder. So you see what you see.
What I -- a baby boomer -- see is a young, vibrant 23-yr-old woman who wears the fashions of our times. Baby boomers also went through a hip-hugger, mini-skirt period, by the way.
When Kelly arrived for the show, she had an elegant hairdo, and was dressed in a lovely, plain gold satin gown with a fashionable -- by today's standards -- bare back. In case you think this is something new, in one of her movies from the early 1960's (with Rod Taylor), Doris Day wore a gold, beaded, tight bare back gown. It was very comparable to the one Kelly wore last night. As I recall, no one ever mistook Doris Day for a slut.

BTW, bikinis on any beach around the world are more revealing than the costume Kelly wore for her performance. So I guess to you any woman in a bikini is a slut. You wouldn't be an Islamist, by any chance, would you?
Oh really?
Well if this offends you ... 
... then Heaven help you if you ever run into Courtney Love. 