Maybe this could be an option, in combination with proficiency you would have several "elements" a caster can use. There are offcourse fire, ice/water, air, earth and electricity. A caster needs to learn the secrets of one of these elements to be able to use them, let's say in the beginning of the game a teacher wishes to teach you one of these secrets for free, later magician teachers will ask a fee, the more of the elements you learn the bigger the fee. This way the caster can learn whatever elements he wants and train them (proficiency) But mastering all of them would take lots of time, training and money.
Now, a caster could only activly wield one element at a time: a passive skill that needs activation. There are also a standard set of spells that can be applied to the active element. These could be, Bolt (quick strike), , Ball (has splash damage), blast (sprays the element (inferno, chainlightning)), apply (Imolate, freeze...) Shower (meteors, ligthning storm, hurricane, snowstorm), with some deviations. These skills come avaible if a certain % of proficiency is reached.
In melee combat a similar system, depending on what weapon you equip the proficiency will rise, unlocking the weapons special abilities. You'll also need to learn the weapons specialisation to be able to use the special skills for it. When equiping a weapon without the specialisation, your proficiency will increase at a much lower rate.
Profiency increament would also be dependant on your level, while you still gain experience in the classic way, so you won't be "grinding" for proficiency.