Math with mr checks never matched what actually happens in game indeed.
Sometimes you will need a lot of mages casting blindness, but sometimes first casting penetrates magic resistance and kills SC.
My friend once ran some VotD checks. It took him lots of tries to actually penetrate MR of a pretender God, just as math suggests. Later his opponent killed 2 of his SCs within three turns, with three to five attempts, dont remember exactly. Etc, etc.
Thus, rather high possibility of a F1 mage with Alteration 2 researched crippling/killing your pretender or equipped raider is hardly a good thing. Random element must be under control; imagine chess where Pawns can retaliate, killing attacking Queens and Castles by rolling 20. Pwns!