Re: Video of Seichiro Endo Shihan
I agree with Mr. Ledyard that Endo Shihan wants (probably) a certain style of ukemi, but he generally does not, in my experience, verbally explain it. Instead, he conveys it by resisting your attack in the same way as Mr. Ledyard's description of Mifune. If you grab him and he is stronger than you, he might just not move. If you then stop your movement, you will probably get his fingers tapping you on your face. This encourages people to get soft and heavy and to not stop moving.
I haven't seen the video but this might be why his uke moves around him. Also there are different degrees of heaviness and the point in the video that some are finding fault with may just be a less experienced uke and Shihan is not going to necessarily move just to "enact" a fight scenario. Waysun Liao once told me that sometimes people see two old men playing taichi push hands lightly not realizing that the two are passing thousands of pounds of chi back and forth. I think that this is probably where Endo Shihan and his top student, Shimizu Sensei will end up.