Ok, so I can say Redbull only started winning when Vettel arrived. There have been so many discussion that Vettel's success was because of Adrian Newey. He timed it right, I would say the same for LH. Mercedes was already trending upwards of becoming a top team, plus the new engine rule would benefit them more so(they pushed hard on the rules). Lewis was smart and jumped ship to join Mercedes at the right time. I would say his wins in 2013 came from the 3 years of development from Brawn and MS. By the way Mercedes was well integrated in McLaren, expanded their relationship in designing and building their own road production car(Not like McLaren F1 and BMW).