Rossi and Kato rode well but didn't win in their first year in each class series. All their championships came in the second year, and they are exceptional. It takes years of experience for most riders.
P.S.: Rossi was champion in his first year of MotoGP, but since it was the first MotoGP anyone who won could say that.
P.P.S.: I wouldn't be at all surprised if NH improved dramatically. Nor would Honda, I'm sure. He's showing good sense creeping up on the limits. Rubber side down forever!