Let's consider these Grand Slam h2h's Becker lead Lendl a whopping 5-1 in Grand Slams. 3 of the matches were at Wimbledon (Becker's best and Lendl's WORST surface), NONE were at the French. Meanwhile, Becker was 0-3 vs Wilander in Slams. 2 were at the French, one at Australia. Now almost nobody would argue that Wilander was better than Lendl, yet Becker did way better against Lendl in Slams, because the surface suited him in those matches. Wilander wasn't good enough to make Wimbledon semis and finals, so Becker never had a chance to improve his Slam h2h against him. There's just no way Nadal would be 4-0 against Federer at the US Open and he's 1-2 against Federer at Wimbledon.