Isn't this kinda similar to The Law of Ueki?
I always thought that having only one power but using it to do different things with it is more interesting than having every single magic/skill in the book.
It also doesn't make the character OP (sadly the magic level of this guy seems to do just that,though),
so I guess we'd have to see how this evolves. Maybe he won't be able to increase his magic power more than that and will become a small fry later on,using his wits and trained ability to make up for it (similar to how Tokine works in Kekkaishi).