Whatever their treatment is, it does have a strengthening component: Shell Game was said to be able to swap small objects, not whole people.
But it also, like I said, seems to be primarily focused on broadening abilities. Owl had vines before, but Vine Clone Jutsu was new. Ete created fire weapons, now she creates fire soldiers. Pritemps made plant cannons, now he can just transform existing plants into them instead of having to make something from scratch. Presumably, Shell Game didn't have this level of range before.
Power's research seems to be focusing on making people more flexible, rather than 'stronger'.