To give you an idea of Tatum's greatness, there is a quote from his contemporary, Fats Waller. When Tatum walked into a club where Waller was playing, Waller stated "I'm just the piano player, but tonight, God is in the house"
"Every Monday piano players would start gathering about nine or
ten o'clock. Tatum wouldn't show up until maybe one or two in the
morning and by the time he got there all the heavies would be
shootin' their best shots. So after a while, after everybody had
played, Tatum would get up and give everyone a master class on
how it should be done."
Billy Taylor, quoted in W. Royal Stokes, The Jazz Scene (New
York:O.U.P. 1991)