I like this video because you can see weapons and empty-hand together. I think looking for a visibly unbalanced uke is not going to illustrate what is going on; O Sensei is throwing his partners without the visible unbalance. He also demonstrates some movements when he starts and some movements when he responds, so you have a collection of interaction that transcends the "who goes first?" chronology question. For me, this means the ideas of "cutting first" or "moving first" are less relevant than cutting [with aiki] or moving [with aiki].