At EURO2013 a sharp pain appeared quite suddenly when Plushenko was doing the Luz, and he said in his interview he almost could not feel his leg. That is the back injury bothering, not the declining jumping ability. If he is healthy, he could perform multiple quads in practice. Yana said in Summer in one of the practice session, he performed over 40 perfect quads. So his "declining" jumping ability is purely due to his injury.
I do not understand CSG (or I understand what he is trying to do too well). Here people asking a question: Can Plushenko win? And we all get it from CSG that he could not, but if other top skaters all fell apart, and Plushenko goes clean, he could medal, not gold. It is OK, it is CSG his own opinion. But why continuing "correcting" other people's opinion by trashing Plushenko's skating ability, reducing him to an average skater (probably even worse than average if not for his consistency). Now he claims that Plushenko probably wouldn't go clean even if he is healthy. That is just so nice of him, reducing a great skater to nothing. And even when the topic went peacefully to discuss about other things, he would drag all people's attention back on how average Plushenko is that the only chance he has on podium is all other skaters bombed.
This makes sense! Of course it would explain why something could be done at one point and not another! Like a lutz toe combo in a practice but not in competition. Or in warmup but not in competition. He gets a sharp pain while doing lutz still lands it but the pain shock causes him to lose the landing of the 3A!