Usher filled a void after Michael's prime
It wasn't as innovative as MJ, he wasn't a crooner like R.Kelly and he wasn't provocative like Prince.
but he did fill that gap and he delivered consistently, gave us big hits but groundbreaking? innovative?
He didn't stand out

The only thing Mario, Chris, Omarion, Ne-Yo have in common with Usher is that they all sing and dance

and I'd say Chris is more innovative than Usher