With radial acceleration the goal, it's nice to have a radius (straight left arm). If the left arm is allowed to bend, the stage is set for a form of longitudinal acceleration.
Yes, and yes.
I'd say swingers would have a much easier time losing extensor action and still have the ability to play well, although I'd never encourage it. At least centrifugal force will bring everything into alignment. But with hitting, we don't have that luxury.
We haven't even talked about the physical implications of the heavy club causing a hyper-extension of the left arm, which is highly possible if extension is re-gained around impact.