I asked a well know stock maker about plywood and stability. He told me that its no more stable than a well dried piece of walnut and still moves (at least Rutland). He uses both materials for his stocks. Not what I wanted to hear hunting and shooting in the coastal rainforest.
Methinks your well known stockmaker prefers to work with/sell high grade walnut stocks. Yes, inadequately sealed laminates will still absorb/expell moisture and therefore will still shrink/swell, just as inadequately sealed walnut will do, but the laminate is much less prone to warpage.
