In general I agree though, the two pronged attack or having two riders high on GC is an advantage, one usually has to end up sacrificing for the other. if Sky rode more conservatively they might have ended up with three riders on the podium in some of the previous Tours instead of two but even two is a bonus. Where it doesn't work is in a race like the 2011 Tour where the Schlecks seem more concerned about finishing on the podium together than cracking Evans. When they woke up and Andy went long range on stage 18 it was all too late. Evans was just waiting to pounce in the TT which he did. The big mistake was turning the race into a match race with Contador and disregarding Evans completely until too late. Evans basically sat in the top four for the entire race until the TT never far off on time. Not sure what the Schlecks and their DS were thinking. They really messed up their tactics that year............but the brothers both got on the podium ! Contador had already ridden the Giro and Evans in the form he was in that season was always going to be more of a danger to Andy than Contador. It was a total misreading of the race by his team.By the final week, agreed, he wasn't close enough, but as pointed out here, he sacrificed his own chances on the Peyresourde stage to take a pull that ultimately achieved little; he didn't crack anyone, but gave up the leverage the team had of 2 riders positioned high up on GC. It wasn't his job to crack himself, it was the job of other teams to crack him. No wonder his DS was so mad.
Again, my analogies above aren't perfect (analogies never are), but are more intended as case studies from which lessons could/should be learned. And it appears that not all the lessons were learned.