On one hand, bio power armor gives you an edge in mass and possibly strength. On the other hand, if the skeleton is moving, it's animated by magic, and who knows what the limits of its magic are.

Also, while skin is "armor" of a sort, it's pretty pathetic armor. What were some of the earliest knives used for? Cutting flesh, a.k.a. bio armor. What were some of those early knives made from? Bone.

And your bio armor: what is it protecting? Vulnerable blood vessels and organs inside the body. What vulnerabilities does a skeleton have? Probably none?

Then there's tendons. Your knee bone's connected to your thigh bone, as the song goes. How? Tendons. A skeleton lacks tendons, so theoretically it's a lot easier to disconnect a skeleton's bones from each-other. But, then again, magic.