Ok, I'll explain how it's a load of crap.
I've recently been training a couple of juniors. I often play matches against them and I'm still undefeated
That means my winning percentage is 100%, now does that mean I can beat Roger and Rafa? I mean look how good I am I can't be beat by these guys so that must mean I can beat anybody right?
Now do you see how stupid your point is? His winning percentage comes from beating guys not named Rafael Nadal or Novak Djokovic. If he had to deal with these 2 guys being the same age as him, he would have a LOT more trouble winning majors, he certainly wouldn't be going on his merry ways not to mention in your stupid analysis would he be winning the grandslam twice.
You got your own analysis wrong too btw. You said you would compare them at the equal age. Well in 2005 Nadal was 18 turning 19. That means you need to put Fed at 18 turning 19 in 2005, 19 -> 20 in 2006, 20 -> 21 in 2007. Therefore, no way he's getting WIM 07 pal. There's one wrong thing you got already.
In your hypothtical situation, it would go like this:
2005:
Rafa, Fed(2000 equivalent), Novak(2006 equivalent) 18 -> 19
Rafa >> RG , Fed >> 0 , Novak >> 0
Slam count: Rafa = 1, Fed = 0, Novak = 0
2006:
Rafa, Fed(2001) & Novak(2007) 19 -> 20
Rafa >> RG & WIM, Fed >> 0, Novak >> USO
Slam count: Rafa = 3, Fed = 0, Novak = 1
2007:
Rafa, Fed(2002) & Novak(2008) 20 -> 21
Rafa >> RG & WIM, Fed >> 0, Novak >> AO & USO
Slam count: Rafa = 5, Fed = 0, Novak = 3
2008:
Rafa, Fed(2003) & Novak(2009) 21 -> 22
Rafa >> RG & WIM, Fed >> 0, Novak >> USO
Slam count: Rafa = 7, Fed = 0, Novak = 4
2009:
Rafa, Fed(2004) & Novak(2010) 22 -> 23
Rafa >> AO, Fed >> WIM & USO, Novak >> 0
Slam count: Rafa = 8, Fed = 2, Novak = 4
2010:
Rafa, Fed(2005) & Novak(2011) 23 -> 24
Rafa >> RG & WIM, Fed >> USO, Novak >> AO
Slam count: Rafa =10, Fed = 3, Novak = 5
2011:
Rafa, Fed(2006) & Novak(2012) 24 -> 25
Rafa >> RG, Fed >> WIM & USO, Novak >> AO
Slam count: Rafa = 11, Fed = 5, Novak = 6
2012:
Rafa, Fed(2007) & Novak(2013) 25 -> 26
Rafa >> RG, Fed >> AO, WIM & USO, Novak >> 0 (We are yet to see his 2013 USO form though, but I highly doubt he'll have better WIM form than 07 Fed)
Slam count: Rafa = 12, Fed = 8, Novak = 6
OK? That's how it would pan out, you compare their equivalent form of those tournaments. The year win % has no bearing on it whatsoever.