Glocks are made from polymer. Never seen a polymer rifle stock. If you are refering to the cheap injection molded plastic stocks, then I prefer walnut. The cheap plastic stocks are more weather resistant and tougher than wood, but none of the plastic stocks are lighter than wood. They are the same weight and are often much heavier than the same rifle offered in walnut. There is a reason why Remington offers their Mt. Rifle in walnut and not the cheap plastic. They tried a couple of versions over the years, but all were heavier than the wood stocks. Same with the Savage Lightweight hunter. If you doubt me you should start weighing some guns and stocks on postal scales sometime.
The better stocks made from fiberglass or Kevlar are a different story. I much prefer them to walnut. I've had too many walnut stocks split, crack, warp and lose zero to ever trust one on a serious hunt. I have a few safe queens in walnut that occasionally get to hunt, but most of my rifles are stocked in McMillan's, Brown Precisions, or High-Tech specialties stocks. The good stocks are up to a pound lighter than either plastic or walnut, are much stronger, stiffer, durable and accurate than either. But they ain't cheap.