[William]

I just noticed that you said there are entire college and societies for the learning of magic.

It seems like the individual nature of each person's magic might really be more fluff than anything else. A flexible magic system can still allow for using, say, the Energy realm or the Light rune to cast a simple Light spell, but one magician whistles a jaunty tune and plucks a drop of rainbow down from the sky, while another pulls the air aside, flicks a switch that's there for a moment, and has a light bulb turn on above his head. Mechanically, they both rolled the same thing but they probably could communicate their magical styles.

...styles! Oh hey. GURPS Thaumatology: Magical Styles. You could have a standardized magic system but every person has their own self-designed magical style, of a type you prefer, with a selection of perks and such. They interact as normal, which would mean that it would be advantageous if sometimes difficult for you to learn enough about some particular opponent's style to have an advantage dealing with them. You immediately give a mechanical flavor to the notion that everyone's magic is individualized.