^ The WW or modern FH can be hit with an Eastern grip. Federer does it all the time. You may be mixing up wrist flexion with wrist extension. The latter is laying the wrist back. Flexion is in the opposite direction. The wrist does not have to been unc0cked in order to pronate the forearm.
Note that you incorrectly referred to pronation as "wrist pronation". It is the forearm that pronates -- ultimately it turns the hand holding the racket. If you are going to call it something other than forearm pronation why not refer to it as "hand" pronation rather than wrist pronation?