Yo-Yo Ma is the world's most popular cellist. That is not to say that he is the world's finest cellist. The Finnish virtuoso Anssi Karttunen, for one, can more effectively make Elliott Carter's Cello Concerto sound like music than can Ma, although it was written for him. Others play bluegrass, tangos and Kyrgyz traditional music more authentically than he.
I'm not sure what to make of this, either. Is the author suggesting that Ma isn't the world's finest cellist because in every area of music that has inspired Ma to take up his bow, he isn't the best? Or is he somehow suggesting that Ma could only be the world's finest cellist if he was the best in every one of those genres?
And what of the Carter concerto? So what? Lots of great musicians are great at some music, and less so in others. You want to hear some great Wagner? Georg Solti's your conductor. You want to hear some great Berlioz? You're better off avoiding what little Berlioz Solti recorded, then.
I'm not arguing that Ma is the world's greatest cellist, or that he isn't. I find the idea kind of weird, anyway. Surely he'd be on the shortlist of the world's greatest cellists, anyway, so this graf is really pretty meaningless except as a way of giving the writer a way of demonstrating his musical street-cred. The whole review is pretty odd, actually; the critic seems to put a lot of stock in stage mannerisms, even going so far as to describe the way Ma walked onto the stage. Heavens, who cares?