1) Songwriting doesn't mean just lyrics. It's the whole song, including music.
2) Michael's songs aren't "just beats". Are you even serious about this? I am pretty sure MJ's songs also have melodies, harmonies and lots of other elements that make a song complete. And he wrote some of the most memorable songs in popular music history.
And if he didn't have a concept/opera album, back masks, "sound bites of things from pop culture" (I assume you mean sampling) that means he cannot be a great songwriter? You have an interesting view of what it means to be a great songwriter, but I disagree that any of those elements are needed to be a great songwriter.
As for the lyrics. Like Barbee said, sure there are better lyricists than Michael, but a song isn't just lyrics. If it was it would be called a poem, not a song. In case of a song music and lyrics have to work together and convey certain feelings in the listener - be it happiness, be it thinking about something, be it sadness etc. There are songwriters who are stronger in the lyrics department and there are songwriters who are stronger in the music department. Michael was in the latter category, it's probably no coincidence that he tended to write the music first and then he wrote lyrics to it. He was more a musician than a poet. But the bottom line is that the music and the lyrics work together. A song does not need to be a poem to be just as or even more powerful. In a song the music and the lyrics have to achieve together something. And if the music and the performance of the song is good then the lyrics do not necessarily need to be compex to achieve an artistic goal. That's actually the beauty of a song: that it's so much more than just the words in it.
And black music is more music focused than lyrics focused. Black artists tend to express deep feelings and thoughts more musically than lyrically. That's more in the black tradition.