Every time I run into a bonewalker I cower in fear because it will damage my strength beyond belief, forcing me to drop half my inventory. Now that I'm in a later stage of the game I have the same with some of Dagoth Ur's kin (the ash vampires), which makes it nigh impossible to defeat some of them.
If my memory serves me well, these effects were temporary and a damaging spell is never temporary. It's greatly annoying having to drop all my armour and most of my weapons, having to run to a shrine in order to fix my attributes and later retrieving this equipment again.
This particular ash vampire, Dagoth Tureynul, also seems to have some kind of instant death spell. It paralyzes me, and before I know it I'm dead, while the moment before my health bar was full.

#1
No, It is correct the way it is! It should indeed be damage attribute. You can fix yourself up at a temple. Try putting your own summoned creatures between you and it!
Edit: They normally only do something like 2-3 points of damage attribute per spell, how bad is the damage you are facing?