Gielgud, In Spite of His Othello?

Stanley Wells was asked who, in his opinion, were The Ten Greatest Actors. I like how right off the bat he dismisses Burbage, not because he wasn’t any good but because frankly we simply have no evidence. He starts with David Garrick, for which there is plenty.
My title comes directly from Wells’ blog, because I have no idea what it means. Did Gielgud do a famously lousy Othello, or something?
The rest of our favorites – McKellen, Dench, Jacobi, Branagh, Scofield… all make the list. Who, in Wells’ opinion, is the greatest? He does say, but I won’t steal their thunder. You have to look for it though, because he drops an understated “for me he is the greatest” in the middle of the article and you’ll skim right by it if you’re in a hurry.