I think they are the two highest ranked players. Give us a solid year of fast surfaces and that would be corrected I think. Let me acknowledge however though that Djokovic and Nadal are both unbelievable at what they do. I just happen to prefer Federer's and Murray's game because of their shotmaking and variety.
So, what you're saying is, if ALL the surfaces were very fast (giving advantage to Fed and others who prefer fast surfaces...big servers mainly), then the highest ranked player would TRULY be the best. That makes no sense. How would that be any different than having all the surfaces slow, like we have these days. What you would have then is simply the reverse of what we have today. That doesn't mean that quality of tennis is any better, or that there is more variety, or that players are more deserving of their ranking. Certain players would be at an advantage and others would struggle. Now you see long, grueling baseline play, and in that scenario you would see Karlovic-like matches with plenty of aces and serve and volleys. There would be no more variety than there is today.
They should have a good MIX of fast and slow surfaces, and then you could argue that highest ranked player is TRULY the best. However, even if they had a good mix of fast and slow surfaces, rankings wouldn't change much. Sure Nadal and Nole wouldn't be so far ahead of everyone else, but the Top 5 will still be ranked as they are now imo. USO is still pretty fast and Rafa and Nole won that tournament (Nole was also in 2 finals). FO is arguably faster than some hard courts and Nadal keeps on winning it. Dubai is one of the fastest and Nole won it 3 times in a row. Paris indoors is probably the fastest court on tour and Federer struggled every time he played there, only managing to get a win last year. Nole also won Paris indoors few years back. Like I said, rankings wouldn't change much even if we had a good mix of slow and fast surfaces. Only difference would be that Rafa and Nole wouldn't be so far ahead of everyone else, like they are now.