Novak’s problem is that he didn’t ascend to #1 until 2011, when he was already 24 years old, by which point Federer’s level had already dropped off a cliff. Federer had already started to lose in slams against 2nd tier guys like Delpo, Berdych, and Tsonga that he used to destroy when he was in his prime. That made it feel to most observers like Djokovic got to the top spot only due to Federer’s decline.
Then he let Murray take him out in 2 slam finals, something that never happened to Federer.
I would not call it problem. Federer became No1 when we was 23, and Nadal when he was 22. For 3-4 years, before he was No1, only Nadal and Federer were better ranked, so, only ATGs.
Story about Federer "declining" prior to 2011 is, to me, total nonsense. He wasn't declining, but younger player (Novak, Murray, Delpo) were emerging, plus Nadal as already emerged. I mean, it would be silly to say that player, accepted as GOAT from majority, started to decline when he was 27, 28, 29. Short domination, right?
And regarding Murray beating Novak. From some point yes, I still think those 2 GS should be something that Novak had to win. And if there is something that I can call as his problem, that would be those 2 slams.
And regarding topic, there is one player I've always afraid, as Novak's fan - Wawrinka at GS. Nadal on RG has beaten Novak many times, but when clay season starts, that's totally other sport, because of Nadal, so my expectations are different. But in general, taking most of the tournaments, I'm only worried when it comes to Novak matches with Stan.