I still haven't read anything in this forum that convinces me there is a problem that needs fixing. An overpowered mage for me would need to be able to win each match regardless of player skill. An example of something like this from another game was provided earlier for A Few Acres of Snow. A game strategy was discovered that every player could use to ensure a victory.
I don't think that's a useful definition of 'overpowered'. Its an even stronger requirement for something I'd consider 'broken', not just 'overpowered'.
To me, 'overpowered' just means that something is a stronger option than any other option. E.g. imagine two Mage Wars spells with identical costs from different schools, except one is dealing an additional die of damage. That's for me an example of 'overpowered', i.e. it's strictly better than a comparable option, but you still may prefer the weaker option because it provides better synergy with the rest of your spellbook.
Regarding your comparison with 'A Few Acres of Snow', the story I heard about it was a bit different:
A top player had discovered a strategy that he claimed would always result in him winning. While the designer didn't believe it, the player kept winning almost every game. Other players tried to adapt the strategy and found it to be very strong but weren't nearly as successful, because the strategy actually also required skill.
Also, said top player typically still managed to win if other players tried to use his strategy against him.
As I said, that's just the version I heard. I haven't been that interested in the game, so I don't know which version is closer to the truth.