... doesn't have the full under lug, but some have them. Although I'm not sure why you need it, plenty heavy the way it is.
The under lug just does not provide weight to control recoil. The weight bias forward enables a more steady aim as observed in Olympic Rapid Fire pistols that actually have movable weights on the barrels to give an appropriate muzzle heavy effect. So, even in a .22 Rim Fire, under lugs provide an advantage in a more steady aim.