Any bowler that points their elbow down the pitch is going to straighten their arm considerably because of the rotational force on the elbow from the fore-arm at delivery. If you brace the elbow, it won’t bend, and the wrist will be able to do the necessary work. But it proves precisely nothing.
A throw, incidentally, does not gain power from the straightening (try throwing with only an elbow bend – it is called a girly throw for a reason). It gains power from the rotation of the elbow, and the whip of the hand. We ought to no-ball bowlers whose elbows point down the pitch.
I don’t know if this video is proof, since it’s from baseball, but man, I’d really not like to face him at the crease:
UPDATE: I saw this via James Fallows, who wrote about the ‘kinetic chain’ — i.e., the force of a good throw — some years ago. This is what he says a ‘girl’s throw’/'poor male athlete’s throw’ involves:
1) Body directed straight-on toward the target as the throw begins, rather than turned 90 degrees (or more) away;
2) Elbow lower than shoulder as your arm comes forward;
3) Wrist inside elbow (closer to your head) as you release the ball and/or palm facing up, giving a pushing rather than hurling motion. Now you know.
Other than (2), don’t fast bowlers violate these rules? They run straight-on (most do, anyway; no one knows just what Malinga does), and they release the ball palm facing up. Right?