Kirin itself doesn't require chakra. Zero chakra. It can be used with one, but without it is the proper way to do it; Sasuke acts as a rod to attract natural lightning and it lactches onto him. Naturally, EMS Sasuke should have been able to Spam it with ease. Kishimoto probably huffed something ... and forgot. Or his editing team made him power Sasuke down. I am betting the second one is far more plausible, as the second Kishi is somehwta fully incharge, he always favours Sasuke; cue to Burt: The Movie.