Excellent point, for all its power the volcano was indeed a desperate "LET'S ALL DIE TOGETHER!" move, plus it could only work in GK itself since there aren't that many dormant volcanos in Erfworld, while Kingworld had zero drawbacks and there's no reason why it can't be pulled anywhere anytime. Ah wait, there's a mention of big juice cost, but that's really meh compared to blowing yourself up with your enemy.
And can't forget the maphack table that although gave GK a massive strategic advantage, also demanded three precious mancers to be unavailable for anything else 24/7.
Then there was also Wanda frying her own brain due to not being careful enough while dabbling in thinkmancy, and that was fate-protected super-talented Wanda. If she could mess up that badly, anybody could. It was a great story element that could explain why most mancers hesitate to try out new stuff, they could suffer terrible backlash if they slip. But did we ever see any mancer fry their own brain while trying out new magics or even just mentioning it? Nope. Instead there's a magic arms race where suddenly everybody's trying to outdo each other and there's no more risks, no more drawbacks. Well, there was big think blowing itself up trying to hack the arkenpliers, but that one should've been already dead and pulled more hax in a few strips than the rest of the comic put together before going out with a bang.
So yeeaaahhh, I can totally understand why you decided to just fully skip mancers with your Erfworld game.