That's a technicality as Nesta's votes were split between two categories. Plus, most of more all-rounded CBs went into the first category anyway. He's not a match to Kohler or Nesta — he quite comfortably sits in the second tier alongside the likes of Stam, McGrath, Vidic etc. Which is still very good, but not actually GOAT.
Then why did you put him in a back 5? Koeman is great for certain systems, and he's certainly among the very best centre backs to ever play the game.
This one doesn't get the best of him in attack (he only has Gullit to send his beautiful diagonal passes to and the middle is insanely crowded as it is) and doesn't get the best of him in defense, with a quite defensive set up & a tough number 9 operating in his zone, while he was always better at preventing the threat way beforehand rather than actually getting into duels, which he quite often lost.