As said, Robben AND Cech were bought by Ranieri before he left, he had a fantastic team and it was largely that team which won the title. In the first title year it was also Gallas/Terry who played more than Carvalho if I recall.
Ferreira is literally crap, he barely plays and looks truly awful when he does, he has played more than Bogarde, but been paid probably 5 times as much, worst buy ever at Chelsea tbh.
Mikel, another player MANY clubs were after and he was hijacked after Utd bought him, Malouda was considered a great prospect by many clubs, he was utterly utterly woeful the entire time Mourinho was there, he only for really 6 games last year looked worth his price tag, he's been pathetic this year and in the past 5-6 games, again can only score when the team is playing well, he can't turn a game on his own, he can't be the difference, he can only perform if the other 10 players are already making the other team look bad.
Cole, wasn't exactly an unknown, and Mourinho rarely if ever got the best out of him, Ballack was one of the players consistantly given as a reason Mourinho left, as in Ballack was forced on him by Abramovich.
EDIT:+ Cole for 5mil doesn't need explaining? Cole for 5mil + gallas, their best defender at that stage, didn't Mourinho fail to win anything after Gallas left and Cole joined? Yup, Gallas involved in most games every season, they win the title 04/05, Gallas starts the 06/07 season at Arsenal and Chelsea didn't win the title that season until last year. So he took apart the best defence in the league, and failed to win anything afterwards, yes Cole is a great left back but Gallas was HUGE for Chelsea.
His list of successful buys, from several hundred million spent, is pitiful. With Real Madrid, very hard to know who was in charge of the deals, for 15 years + its been the boards decision who came in, they probably ask for some input, Carvalho is probably the only player he had real influence over.