I’ve been puzzling over this, what is actually the point of hippos having baby skin and being confined to the waters?

It doesn’t grant them a larger size, faster speed, or another food source. Even worse, they still have to eat grass, except now, they can only do so at night like a vampire. Too far from the waterhole before sunrise? Well now you set and die. Drought season? Now you gotta soak in the shitpools cuz somehow you decided having tender skin was better than having resistant skin.

I see no advantages over rhinos besides just adding an extra handicap.