Right now Murray is better than Nadal who doesnt even play professional tennis any longer (he has been gone long enough we can say this until he actually does come back), and IMO better than Federer now even if Federer has the edge on the computer points for the moment. Of course he will be talked about as part of the big 4, he is probably the 2nd best player right now, and still has a great shot at a #1 year in 2013, and I am not even a Murray the way I am a Nadal fan or to a lesser extent a Djokovic fan. As for his career, he is light years behind the big 3, but light years beyond anyone else currently playing (discounting corpses like Hewitt). Del Potro also has 1 major, but the other aspects of their career are in another universe.
In the last 5 years the dominance of the top few isnt just slams, it extends to Masters, where nobody outside those 4 has won more than 1, and scant few at that. Murray has managed to win 8 Masters since 2008. Also nobody outside those four has managed more than 2 slam finals (and I believe Soderling is the only one who did that), while Murray has 6 in the last year alone. He has been ranked above all of Nadal, Federer, or Djokovic at various points in time. He has been the bottom rung of that group for sure, but it also does seem he has been more a part of that group, then a part of the Berdych and friends one.