Personally I don't have an issue with the retcon, it needed to happen, it makes sense of the weak introduction, and while it may be a bit of a "weak" explanation it's not one that's really contradicted by anything I can think of.... To be honest it also makes some sense of the ninja war nonsense that went down the way it did in some cases if I choose to believe Kabuto used the weaker version for some of his characters... which I do... lol