I've often noticed that while Michael Jackson wasn't always the first to do something, he was often the best at it. A great example is the moonwalk, many people though Michael invented it but he didn't. Regardless, he was by far the best at it. I've never seen anyone come remotely close to his moonwalks. The lean is another great example! People were doing it for decades before him, but I've never seen anyone pull it off as great as Michael. He does it in a way that feels natural, like you could get off the couch and do it right then and there ... but you can't! I saw a Bollywood video about 15 minutes ago where the main singer out-did Michael in the sense that he leaned even further than Michael, but it didn't look natural. He pushed it too far and it became obvious he was using wires. I never got that feeling from Michael. He makes it seem so... effortless.
I don't think you always have to be the first to do something (even if it absolutely helps and is significant in itself), but definitely being the best at it is significant too in my opinion. Sometimes those who do it first are the best, sometimes not.