We have to be careful to get the logic sequences right, or be hoisted on petards by fanboys. What is known, and guilt by association.
For example, Leinders and Sky. It is known Leinders was a doping doctor,and given Sky's modus operandi and Wiggo statements why would they hire him. Guilt by association? They could hire any other doctor in the world.
Evans and BMC? It is known BMC had a murky history. But Evans is not at liberty to join a clean team, because they are all to some extent murky. He needs to join a wealthy team with solid teamwork, especially after Lotto. Time is running out, he is getting older. BMC is a perfect fit. Guilt by association? Not the same as Leinders, because we also know not all riders are dopers, even if others within the team are or even if the team is systematic. Bassons and Moncoutie are the prime examples.
Has Evans performance improved at BMC? Not one iota. He is remarkably consistent throughout his career, like a normal person. He improves each year, plateaus at 30 for a few years, then begins a gradual decline that will become steep shortly, or he retires. He gets two seconds, a crash year, wins worlds through guile, wins Tour through bloody mindedness and Contador imploding, that's it, he is done.
Sure ask questions, but don't make absolute judgements unless there is some proof of some kind, circumstantial or otherwise. In Evans case there is none. Look at a comparison with Wiggo this year. Not a single similarity of suspicious performance. No ridiculous team, no secret training, no superhuman season endurance, no "marginal gains" rubbish to deflect attention, no rollers for warming down, no new skill sets, no superdomestique, no being within 10 seconds of the lead from day 1 and defending for two weeks, no killing the field in ITT. Nothing! Nothing to indicate a team program, he did it almost totally through his own efforts. So no, BMC has not helped him by being a doper team.