One additional weakness that others haven't mentioned is Enchantment Transfusion. Enchantment Transfusion can counter Steal Enchantment, and Steal Enchantment is expensive enough in actions, mana, and spellbook points that having it countered really hurts.
Overall, if Steal Enchantment were a quick action I would probably include it in some aggressive spellbooks that tend to be action starved because saving that action would be really nice, and I could save up mana for it by hitting things rather than casting. Unfortunately, with it being a full action I just can't justify including it in the spellbooks that would benefit most from the action efficiency.
Wizard can run it, but I haven't seen it used much due to the high cost. Plus most Wizards don't tend to be action starved in my experience, so getting the action discount is of relatively little value.