[quote=@Tyki]
[@Tominas][@Stitches]

It's more a case of the more things you try to do with a spell the weaker it is (I think) so something like a fireball is fairly strong cause all your doing is throwing a large bit of fire while raising flaming zombies is a bit less potent but slightly more applicable to situations. It's a thing of utility vs power I think. Letter Bee will have to clarify as it's his system
[/quote]

It's both; the more Schools you have, or the more Schools one spell uses, the weaker the spell is. However, getting more spell slots by training/advancing the plot gets around that, as you now have more 'space' for spells.