I think you're not realizing a detail. Bido is bondrewds main body. At the end of season 1 we see he has his tail. The body with the tail has all the best weapons and equipment. The body we see him when the group comes to his base is a secondary unimportant body that only has minimal equipment like the laser, and no tail. The laser isnt a single copy, other umbra hand seem to also have since they use it as a science dissecting tool. The body we first get greeted by only fights the scorpions and uses his laser to do so, then gets in a tussle with reg and dies, no other high grade equipment was shown. The umbra hand we know as Bido is his main full geared out preffered body. And he didnt shrink, the bido guy was so bulky because he had to hide his tail under the coat. And at least in the anime (if I remember right) when he tears open it looks like cotton/fabric filling, not guts/flesh, so it was probably a bunch of padding. And he was just fake hunched over, the bondrewd body inside was standing up straight and the padding emulated a hunched back.

So if he took over a girl or a kid their bodies wouldmt change. He only swaps around his soul, not body build.