That's even MORE incredible then, that you don't consider him a musical genius!
I certainly consider him a
rhythmical genius. He was one of those people who have rhythm hardwired from the brain to every part of his body. A living beatbox. But I generally reserve "musical" for the more tonal aspects of music, and IMO his singing and his melodies were not exceptional in any way.
I don't even know on what basis you're saying he's not - on the motown performance? I went for one of his History concerts and he sure wasn't lip syncing - you could clearly hear the exhaustion in his voice, sometimes he would be breathless.
Well, if you google around a little you'll find that a lot of insiders as well as gig attendees confirming that his vocals were pre-recorded to a large extent, both on the History and the Dangerous tour, and it was even semi-officially announced that he would mostly be lipsynching on his upcoming O2 shows. But they didn't use the original recordings, he went into the studio and recorded new vocals for the performance versions. A lot of artists do this nowadays -- Britney, Madonna, Beyoncé... they alternate between live and pre-recorded vocals, and occasionally they'll open the mic feed for speech inbetween the songs or call/response parts where they interact with the audience. That way you get a seamless blend between live and pre-recorded vocals.
It's not really "cheating"; I know all these artists can sing, but with elaborate and physically demanding choreography even the best of vocalists have trouble singing. Try it yourself, stand up and sing one continuous note, "aaaaaaaaaa...", then start jumping up and down on the spot, and suddenly it's "aaaaaaEaaaaaaEaaaaa". Prince is one of the few who can pull it off, but then again his dancing isn't very choreographed, plus he has a very low center of gravity.

Jackson was a perfectionist and couldn't have lived with himself if every dance move and every note weren't perfect, and since it's impossible to get both of them perfect simultaneously for two consecutive hours every night, he had to cheat a little with one of them. And since you can't pre-record the dancing, it had to be the singing.
But he sounded incredible - he didn't have a 'great' voice but it was unique - almost synthetic (which imo, was really cool)
His voice had two modes that I liked... one was the one he used on slower songs in the early part of his solo career, especially on "She's out of my life" which is one of his best vocal performances on any of his albums... the other was when he used his full-on rock voice, like on the Dirty Diana chorus. But I absolutely hated all his gimmicky 'tics', the weird sounds he made inbetween the words. The syncopated "dah!" he threw in everywhere, the trademark "hee-hee" and the peculiar "oooooooooh" scream that came out of the blue for no apparent reason, and my personal pet peeve, pronouncing "come on" as "shamone". I just wanted to kick his ass every time I heard that stupid pronunciation. It bought him the 2nd spot on my top list of "Singers I'd like to lobotomize so they'll stop torturing the world with disgusting sounds". The #1 spot is held by that horrible woman who sang Cranberries' "Zombie". Yodeling + Rock'n'Roll + Irish accent = painful.
I would love to see what your 'musical genius' bar is set at.
I dunno, any truly exceptional songwriter, vocalist or musician, or someone whose
musical contribution changed music history, someone who revolutionized music production/recording or otherwise left a big enough imprint to change music history. I'd place people like McCartney/Lennon, Zappa, Kate Bush, Prince, Collins/Gabriel and even Kraftwerk in that category, but Jackson, well... he certainly changed music history in ways, but IMO it wasn't so much the music itself. It had more to do with his dancing and performances, and that he opened the door for black artists to white audiences by breaking into the mainstream and being the first black artist to be played on MTV. His songs were hardly groundbreaking, it was conventional mainstream pop with hints of R&B and rock thrown in. He brought nothing new in terms of production values, style, song structure or anything that you could identify in other people's music.
Again, if you look at one of Jackson's contemporaries, Prince, you'll find that he had a massive impact at the time. He introduced a distinct sound that was very influential on mainstream music in the mid 80's... you could instantly hear which artists and producers were Prince fans. Jackson didn't have that kind of influence because there really was no distinct Jackson sound. After "Thriller", everything he did was derivative. In fact I'd say "Dangerous" was very influenced by Prince, directly or indirectly... the funky drum programming on "Black and White", "Keep it in the Closet" and a few of those songs can be traced back to trends that Prince established with songs like "When Doves Cry", "Alphabet St." and "Kiss" a few years earlier.
I'd gladly be called a musical fool/idiot to have my songs get the attention of almost every person in the world - young and old. I would die extremely happy.
Are you sure? Look at Jackson... he died more unhappy than your average bus driver or waitress. He is living, erm, dead proof that success is not the key to happiness.