I've never bought this, if Murray played before Federer he'd have been below Agassi and Sampras and so on. He was simply a 2-3 slam player. He started big matches too slowly and his mental game has always appeared apalling.
On the overall discussion, I always had Federer. For me Nadal's record leans too heavily on the French Open when it comes to slams. For Federer, Djokovic and Nadal, if you exclude their wins in their strongest slam they're left with 12, 13 and 8 respectively. His record in the French is to be commended and he is by a mile the greatest clay court player ever, but if someone wins 2/3 of his slams at one event on a specialist surface, it takes away from an overall claim in my opinion.
This doesn’t make sense though, as Sampras and Agassi didn’t have the consistency of the big 4. Agassi in particular had years where he wasn’t a relevant threat during his “peak” years. There was far more scope for another player to pick up multiple slams.
I’d only just have Agassi slightly above Murray in an all-time list. At the point Murray’s hip ended his career at the very top (when they both were c. 30), their comparative figures were:
Grand Slam Titles: A - 5; M - 3
Grand Slam Finals: A - 12; M - 11
Masters/Olympic Titles: A - 11; M - 17
Total Titles: A - 45; M - 45
Murray has never lost a slam final to anyone other than Djokovic or Federer. Agassi similarly struggled against the best of that era (he was 1-4 against Sampras in finals compared to Murray’s 2-5 against Novak) but, of course, only really had Sampras at that level, compared to Murray having to deal with all the big 3.