... the iaido vid is beside the point ...
Did you acutally see the sojutsu kata in what you call "iaido vid"?
Did you recognize the ishizuki of their yari?
Did you notice how they use it?
If so: Why do you think this to be beside the point?
If not: Does a second look change your opinion about the vid?
Your talking of "... iaido vid ...", "... kendo world ... " and "competitive sparring" makes me wonder whether your statment is acutally based in practicing any koryû sojutsu?
I apologize for the question, but my English simply is not good enough so that I could differentiate here between someone just using easy language and someone who is not really at home in the subject.
Now please dig out some videos of the guys in white sparring with identical dummy spears (yes those LONG ones they were using for the kata demo) and see if a butt-strike is ever used. not kata, actual competitive sparring.
I have to admit, I'm at loss: I assume this is irony?