Re: stretched vs. mounted canvas
I don't believe that the move away from mounted to stretched canvas had anything to do with wood's stability or tendency to warp. Stretchers are no less likely to flex and warp; they are in fact made from wood. In fact, stretchers are designed to be adjusted using keys to allow adjusting the tension of the stretched surface to compensate for any flexing.
In actuality, any panel, plywood or not, if prepared properly, is much more stable than stretchers.
As I understand it, the primary benefit of stretching is reduced weight. I personally don't like the bounciness of stretched canvas or the canvas texture. However, I like the fact that a large stretched canvas is very light. It's much easier to hang, store and ship than a similarly sized canvas panel.
When I work small, I prefer canvas mounted on birch plywood. I really like the solidity of the surface.
So, stretched canvas makes large works on canvas much more practical.