Didn't really get the point of the skill decreases for opponents if yours is over 100%. But fortunately Runequest isn't a chess tournament, and you can use which ever rules you like. And any DM worth his salt can restrict spells if their players start distrupting the game with them. I think that I personally will start using the "it's a trance" rule someone suggested. Glorantha is a lethal place, and just being an unstoppable juggernaut to your melee opponents in front of you doesn't make you invulnerable, just shoot Achilles in the heel.
And thanks, Kloster.
e: would there be interest in a thread where people post their house rules?