Actually, I advice you to try to find a few reels about how a guy called Lance Armstrong won races. This was of course long ago, so let me explain.
Lance Armstrong was the best TdF racer ever, he won 7 times, until they took that away. He used the tactic to have his team kill everyone else in the mountain stages by setting up a blistering pace.
Before Lance this tactic was employed by T-Mobile (Riis/Ulrich, also known dopers) and Banesto, the team of Miguel Indurain (the big star at the beginning of the Epoe era)
This is the same as Sky is doing.
Now I think I need to explain cycling mechanics too, as I think it helps you to understand. If I ride in front of you, you need less energy as I do. This is called slipstreaming. Even when climbing, especially at these speeds, sitting in the slipstream is easier. So if your helpers (a team has generally one leader and 7 helpers) manage to drop the other competitors it indicates they are actually stronger than those competitors. This indicates that Sky's racers are a lot stronger than the competition.
Back to history. Prior to the Epo era there were more attacks and the racing was less controlled. There were trains, but they got derailed a lot. This is the tactic Sky is NOT using.
I hope you could follow this so far? If not Youtube can help you understand this beautiful sport.
anyway, the conclusion is that succesful trains are not a sign of clean racing at all. In fact the most succesful cases were based on Blood-doping and Epo. This does not proof Sky is using doping, but it also makes clear that wht mister Brailsford is saying is false. Some would say he's a liar here as he was around when Lance Armstrong won this way.