While I'll be the first to say the M4/collapsible stock stinks, it's not for the reasons you've stated. You can get past all of that and it'll work fine. The issues with the carbine stock are really a fault that is amplified with the shorter gas system/sight radius: it's more critical for cheek weld, and the carbine stock is tough to get a good weld on. I tied and glued para cord on mine in the army, with a knot to hit the corner of my mouth. I'd throw it up, my nose tip would be on the chargeing handle, mouth on the knot, and then I KNEW my eye was in the same plce every time...which gave more conistancy with irons and eliminated any issues with optics and eye placement. Now, I had a LOT of trigger time, too. An M4 still shoulders and points as fast as my best fitting shotguns, just because my body still remembers where it's 'supposed' to be. IMO, just shoot the pee out of it before you go monkeying with the stock. Learn the gun, and it'll tell you what needs fixing. Just my thoughts.
Here's a thought: Let the ducks work and decoy.