GSM Nadull is right (for once). Murray was semi-competitive with Nadal in the past, the problem is he's been going backwards and his game hasn't really improved, not has his mental strength. If he was ever competitive with Nadal, he isn't anymore and his making the Wimbledon and USO finals was all because of the hole Nadal left. In the past, you had to beat 2/3 of Nadal/Fed/Djokovic to win a slam which made it so difficult. Only Del Potro managed to do it and even then just barely (requiring Chokerer to show up). To make the Wimbledon final, he beat Tsonga after Nadal lost. To make the USO final he beat Berdych after Fed lost.
That's not to say his win wasn't legitimate (it wasn't legitimate for other reasons) but it does show he hasn't really had the chance to show improvement. He faced a dead tired Fed in the OG finals (who already had his gold and silver medals), he got crushed at Wimbledon, he actually got worse at MS events, and he choked as hard as he could after being given 2 sets in the USO final in unplayable conditions and Djokovic just ran out of gas. He has yet to show he has any chance against Nadal or that he improved after his USO, showing the same attitude and pushing at the WTF. Everybody goes on about Lendl, but Murray is playing the same and Lendl is probably a similar coach to Brad Gilbert who made no difference for Murray. Personally, I think Murray is uncoachable because of his bad attitude and mystifying pushing style despite his potential power.
I suggest we wait and see what happens in Murray's next match against Nadal. Before last year Murray wasn't beating Fed & Djoker in best-of-5 matches; Nadal has not
been the only obstacle in the way of big titles.