You bring up a good point. Using the wrist too much is not good. I know that there are many players that use a lot of wrist but keeping the wrist kind of straight is preferred for strength. I rather bend my wrist up than down for drawing the bow down. It gives a better smoother pull on bow changes. It's not so much that you should not use wrist movements but more that you shouldn't bend it down too much and not use excessive movements.
Obviously it's good to have a certain degree of relaxation in your wrist but at the same time, a little firmness for power.
Finger flexibility is great IMAO. I have a few videos in which I demonstrate the type of finger flexibility that I think is super beneficial.

After seeing your video and re-reading this thread I realize that the problem is derived from tensing your wrist when playing at the upper part of the bow. The easiest way to alleviate this is to experiment with the angle of the violin so that you don't have to reach so hard at the tip of the bow. It might benefit you to do soft gentle stretches before and after practice. It would be a more controlled way to stretch and loosen your Extensor carpi radialis longus muscle (I really have no idea which muscle, tendon you actually need to stretch).