Yep, that's what I had in mind. Its far from unbeatable, and there are any number of strategies that would render a 'hole in the middle' AMF ineffective, without being particularly strong against the other players (i.e. a tiny opponent could just fly into my character's space, or worse, an Arcane Archer could use Imbue Arrow to hit my character with spell effect without mine being able to return the favor.
Anyway, I'm thinking of bagging the idea since other players are uncomfortable with it. Also, getting into Archmage would eat up a bunch of feats.