I don't know where the idea that Djokovic struggles against big serves comes from, his anti-fans or some people who are truly deeply madly stupid?
vs Karlovic: 3 times, none at a Slam, the most recent time was at 250 Event LOL
vs Roddick: none post-2011
vs Kyrgios: LOL he lost left and right during that period, to all kinds of player
Check his Slam/MS1000 record against other big serves like Raonic, Isner, Berdych, Anderson, Cilic, Del Potro...
How about Roger? Losses to Nadal and Djokovic should be excluded, they're tennis Gods like Roger, their trademark shots don't come from this Earth.. We'll see him beaten 11 times by Murray, beaten by Kuerten on both hard and clay, beaten fair and square on hard by Hrbaty, so will we from now on agree that:
Roger Federer has serious problems with DECENT BACKHANDS.