Especially in England.
When he first came over to the Premier League, the idea of a diminutive technician not only having a free role in the middle but running every game from that position was largely unheard of. You'd get tricky types like Pires and Zola but they'd ultimately become wingers or forwards in rigid 4-4-2 systems.
Silva would surely get muscled off the ball too easily playing in the centre, and surely he wouldn't cope with the pace of the league? By the time he left, tiny creative midfielders were the norm. He paved the way for Cazorla, Nasri, Ozil, Mata, and Coutinho, and outshone them all in this country.
Even Ferguson tried to emulate what Silva was doing with Kagawa, and failed.
Can you remember the last time a new player was accused of "not coping with the physicality and pace of English football"? Silva set the template for players like him, more than dealt with the physicality of defensive midfielders in England, and eventually changed the pace of the English game, making it play to his rhythm instead.