How is it an ass pull? Just because it had never been done at that point? It is much more likely that nobody ever thought about something like that before. I'm sure that B is perfectly capable of it, but doesn't know how. It probably never came up, so he had no reason to know it. Naruto figured it out using it with Kakashi, then figured he could do the exact same with everybody else.
New ability doesn't equal asspull, or plot hole. Only somebody incapable of thought and logic would automatically jump to that conclusion. Thinking is difficult, so it's much easier to assume that anything they aren't sure of is a plot hole.