Singing is and instrument. But he didn't just sing, he used to play the drums and guitar. If you said that he ISN'T a musician, then you would be saying that every other person out there who only sings, aren't musicians either. So yea, I would say Michael Jackson a musician because singing is an instrument.
Michael Jackson was a musical genius. Just because he didn't play an instrument on stage doesn't mean he didn't know how to play them. Many professional musicians play multiple instruments that the public doesn't even know about. Micheal Jackson was a brilliant song writer and musical composer. I have no doubt that he was as talented on actual musical instruments.
Michael Jackson sung. Is this a real question? Whoever is asking this question must not consider every single hip-hop musician not a real musician if they just rhyme or if they just use turntables and beat-makers. The notion that "an instrument" has to be a sanctioned device is totalitarian and insane. You can bang on a kettle and that's an instrument.
Sure, in his performances, he didn't plan an instrument, so based on that alone, claiming he was a musician would depend on what source you used to define "musician".(1) But, if you look at the source, it states that he could to some extent play various musical instruments to some extent. Sure, he couldn't read or write sheet music but no definition requires that skill. Yes, that skill would come in handy but he still composed but by other means. Sure, he may not have been that good at any instrument but that is not a requirement either.
Michael Jackson was far more than just a singer and dancer. Many images and movies of his talents exist. In his younger days he would be regularly seen playing the drums or guitar. Later in life, he could be seen playing the piano. I think if you were fortunate enough to have seen Michael Jackson in concert you would understand why no one cared if he played an instrument.
When we define what it means by being a musician, we need to know a musician does play an instrument. As far as we know Michael Jackson was an excellent dancer and singer who we remember forever, yet he didn't play any instrument at all. Thus, we should not regard him as a musician yet we should rather regard him as a wonderful artist or singer.
Michael Jackson should have been called an artist or a singer rather than a musician. He had a full musical team behind him playing instruments, so he did not need to worry about playing any himself. His image was more about entertainment than skill with guitars, drums, or a piano.