I can't be mad at the suggestion. If only for the sake of not being hampered by needing to fit in the do-nothing healer role with an over-abundance of healing skills and undercooked impact of 2-4% buffs, perhaps AST would have been allowed to have more of a buffing-regimen if they were a DPS, and therefore the class fantasy would have been better off.
As for balance, let's face it: AST isn't BLM, and it wouldn't be a melee class, so the balance just wouldn't matter all that much to SE overall. Hell, at least as a DPS class, AST would probably get more playtesting.

But honestly, rather than just this, I would prefer to have it so that all jobs had the ability to function in as any role by switching out certain spells, skills, and abilities based on the role the player chooses. That way everyone could just be their favorite job(s) whenever.