so EZ,
you're saying that mathematically sound poker is to always raise pre from the bb with A9o against 3 limpers? I'd have to disagree with you there.
you're going to be playing out of position postflop unless the only caller you get is sb. you're hand is NOT a premium hand, it's a playable hand.
using the term "mathematically sound poker" doesn't let us disregard our opponents. almost every decision in poker is somehow connected to what we think of our opponents.
in this case I'm making a generalization about what I think of most players at 2NL and giving feedback based on that. I'm simply saying that I personally like this move in this spot. If he's on the button raise away!
NOTE - I go quite aggro once I've made a hand - again depending on the opponent.