Yet tons of people seem to be going through with pure mages just fine.
With mediocre mage - yes, probably, with INT/Spirit-based mage - I doubt
yet those "medicore" mages made it through just fine, while your "superior" mage can't.
Then again there is a super damage bug going around, but my point still stands.
Like everyone else said: This is not a standard "mage = all INT" game.