He is definitely not the best human that ever walked the Earth though.
Sure, because there is no such thing as THE best human. I did not say he was the best, I said he was the greatest because he managed to overcome temptation and lure of the prophecy. If to compare with anyone in TW world who ever desired power, for whatever reason, I believe his is the only one who was able to walk away because he believed that the way to such power was not worth it. The rest would have found a bunch of reasons to justify why it would be right to fuck a goat if need be, or whatever, if it could make everyone happy, and save the world, while in reality be simply unable to resist this temptation.
By my lights, if the world in order to be saved requires some girl being mistreated, such a world deserves to be destroyed because it is a crappy world ruled by a crappy destiny. So all this fuss about Ciri's savior-child is a POS for me, whoever is trying to do it - the sorceresses, the elves, or whoever. The emperor managed to get out of this stupid chase. Good for him.