High blood magic with both Dead Raiser and Staff of Protection along with high elemental magic skills makes for a pretty effective all-around magician. It also doesn't seem like the skeletors will expire on their own, so they can be put to use as guards, mining escort, advance warning against encroaching enemies (thanks to AI aggro)...

The staff of protection prevents damage done before armor calculation is applied, so that's why it tends to go down so quickly. It should be much more effective against damage that cannot be prevented by armor in the first place (I don't remember how it works against poison and such though), when you can summon many skeletors or have other allies alongside you, as well as when in use with pure mage armor.

I wouldn't say any of the magic skills are intended to be entirely self-sufficient (elemental magic comes pretty close though), and that's one reason why they are available relatively late into the game. You can't leave your sword or spear home just because you stole some magic from your enemies.