Come to think of it - it surprises me how some professional players get away with the high wrist action? I am sure we can all cite world class players who have a high wrist so maybe they are just lucky.
I think they are not lucky. They know to play with minimum effort and keeping a relaxed wrist while pressing with fingers, so some wrist bent doesn't bother them. In my experience internal tension and wrong coordination to press fingers while keeping a tight wrist is normally the case rather than simply a deviated wrist. Puting wrist straight is a remedial thing rather than the actual true solution, IMO. Although sometimes changing wrist positioning helps a lot. But IMO it is not because the positioning itself, but because it challenges your bad habits and perception. When you get a different perspective sometimes you correct some issues unconsciously.
Of course too much wrist bent is bad, but I don't think Segovia or Williams is too much bent. We can see they could reach old age without injury.
A good exercise to learn releasing the wrist is to press something in the hand, like a tennis ball, with the fingers and then move arm in circles and release wrist letting hand shake around, while keeping ball tight from fingers alone. A lot of people start loosing the ball while releasing the wrist. Then they try to hold tight again with fingers and wrist tighten together. It is really not an easy coordination, we are used to tight wrist and fingers together. But we must learn to detach them to get good technique. Check Williams or D Russell, their RH wrist are very loose, sometimes we notice hand shaking free while playing denoting a real free wrist. That is not the case with some other players...
Spine-neck dynamics and breathing is also the other issue.
I think besides stretching, self-massage is also another good think. It helps releasing and relaxing, activates circulation which accelerates the recovery and enhances self-knowledge and perception of muscles. Stretching might be dangerous if you don't do it carefully.
Also pay attention what you eat. Drink a lot of water and do regular exercises, like some walking, to keep good internal fluid circulation activity.