You are absolutely correct. The gun weight to muzzle energy ratio is dominant factor in determining recoil. I own a Colt Defender that came with an aluminum frame that kicked like a mule. Replacing the aluminum frame with a stainless steel frame reduced the recoil to an acceptable level. The other advantage to the extra mass is, it is more stable no mater what stance the shooter prefers, i.e., in now actually hits where it’s pointed.