Mages Are a Game of Extremes Currently
Mage itemization is basically balanced to only provide Mages with the means to deal either more damage or more casting. Very little utility is granted by AP items unless the AP item can almost strictly not be built wisely on most Mages. This is most likely the case because, when compared to most AD Casters, AP Casters provide a TON more utility and somewhat more crowd control. Adding in any more utility would mean utility overload. However, this has left some Mages who aren't the best at damage or utility feeling rather weak. What I mean is if your character isn't either all out damage or all out utility, you will find it hard to function without being overtuned since you will have poor AP ratios and not enough utility to be a threat with utility. Since AP itemization won't help you there, you kind of just become a little bit "dusty" so to speak. You don't feel super useful.