What it needs:
A skill roll to cast. Modified by armour and things that would affect concentration. Probably scrap concentration. Chance of nasty failure. Probably not the simple “it does the opposite” of Iron Heroes.
In Conan terms your Adept level becomes your magic attack roll. This can actually be a neater way of describing power levels.
Schools or trees of abilities. Some might be limited by pre-requisites including magic attack bonus other simply by difficulty.
The question becomes, what can a person attain as a result of entry into this school, what do they use on a daily basis and what is the penultimate goal of this school?
For example, an alchemist gains the ability to identify and craft exotic materials. A sort of epic expansion to the craft skill. Then depending on bent he either cures or poisons folks, strengthens or weakens and transmutes materials. Finally he either manufactures a philosopher’s stone or a Frankenstein-like monster
The most diverse and powerful magically would have 4 skill points per level, poor attack bonus and good will save. 4 feats from lv @ 1st gives say familiar, scribe scroll and 2 spells.