What level, do you mean statistically or the level of play? Statistically he didn't, Fed 2003-2007 was higher.
But, yeah possibly he did reach higher level of play, but that is evolution, nothing to do with Djokovic. Greats in every era were better than greats in previous era.
That's why the level of play doesn't really matter. Roddick reached higher level than Laver, means nothing.
Also we can't even be sure if Djokovic reached higher level, because the conditions are different. Yes on plexi sure, I give you that, but you needed different skills to win in 2003-2007.
Hey if conditions were the same, I would agree that Djokovic reached higher level. Doesn't really matter though.