Hitman
Bionic Poster
Combined with Djoker upping his game even further under Boris after 13. Even without the back injury he was going to need some serious improvement to keep winning slams.
The thing is we will never know how much Murray would have improved though. He reached his apex at W 2013 IMO and was enjoying his rivalry with Djokovic at that time, that period from Rome 2011 to W 2013 was the most intense period of the Djokovic v Murray rivalry. They were going at each other during that time. After W 2013, it all came crashing down for Murray.