I like to think of yonkyo as an atemi, to create distraction and break-balance. Therefore, it should be a sudden thing, not a grip with constant pressure. A surprise, a sudden thing, is harder to resist. It will usually create the distraction and break-balance needed.
I agree. I think a lot of the locks work better as ATEMI than come-alongs.
A combination of influences helped me improve my 4 KYO recently. In one of Saito's books, a TACHIDORI involves catching a descending cut with the palm of your right hand placed under UKE's left grip. Catch him high and you have his balance.
About the same time as I'd brought this into class, I looked at a Tomiki book and they use a 4 KYO like grip as one of their principle practices (we hardly ever do it.)
Playing with these two in class gave me a lot of insight into 4 KYO--it's KUZUSHI and TAI SABAKI--as an attack of the shoulder, not the wrist, and a quite compelling one, too, with or without the pain. (You do it this way, against the shoulderj, in the vid on your web page.)