When Maradona joined Napoli they were mid-table, battling relegation, they became a force to be reckoned with after they bought other players. Maradona's first season in Naples and they finished 12 in the table, if i'm not mistaken.
A world class player is always a world class player. Whether Buffon at this moment in time was playing with Juve or with Cagliari, and putting in the same performances, you'd have to be retarded to say he is not world class