If a full magician is better than an AM, that's a problem. they shouldn't be better at start unless they have higher magic priority(and therefore, a full magician can be better at start, but isn't necessarily.)
The tradeoff is supposed to be that a full magician is more generalised, while an aspected magician is specialized. which should mean that an AM with the same stats is better at their area of magic than a Magician. The same way that a physisist can do something in any branch, but an astrophysicist is still going to kick their butts when it comes to calculating orbital trajectories, even if they can'd compute a biochemical reaction if their life depends on it. Magicians already have the bonus of adaptability. In their own spheres, AM should be as good, or better because they lose that adaptability. or else, there isn't any purpose in taking AM, not because you are a munchkin, but because it gives you no benefit.
To use a lunch based example: If I can buy a footlong sandwich for $5, or I can buy the same type of 4 inch sandwich for $5, Why would I ever buy the 4 inch? It doesn't make me a munchkin or pig to take the footlong, it just makes me not an idiot.
I'm not saying it isn't more complicated than that. I am saying that unless the AM does something better than the Magician, what is the point?