So many could be added to that list:
Kissin - could ANYBODY in history match this guy's speed, articulation, accuracy and control on such a consistent basis? (The answer, BTW, is no).
Katsaris - the best octaves I have ever heard, including Horowitz and Argerich, not bad finger technique too...
Kuzmin - not as well known, but his recordings are out there, Feux Follets, Don Juan, etc. AND (this is very important), as clean live as he is on his recordings...
Valentina Lisitsa - speed, accuracy, control - amazing, she can play side by side with anyone...
I'm not so sure that some of those pianists should be there -
Ashkenazie - great, but I have never heard him do something that was so seemingly inhuman, ala Horowitz or Cziffra or Barere or Katsaris
Hamelin - I know his recordings, but have you ever heard him live? Sometimes (often) it can be a slop-fest...ah, the miracles of modern editing! He simply chooses to play repertoire that many pianists don't, so there is no-one to compare him to - but I'm SURE that Kissin or Volodos could do what he does, if they chose to...
Bartok, Saint-Saens, Busoni - we just don't have enough to judge them by, unfortunately...