This is the theory I have right now. I am trying to work on it and some of the things would be changed to add some of the balance to it. Luck, your ability scores, random chance, in the end a caster could be entirely too powerful if not balanced right but at the same time in the concept of everyone can access magic so theoretically enough people together have the power to bring down someone getting to strong.

It might be that to have the greatest abilities would require superhuman abilities in Intelligence, wisdom, and endurance