AD spellcasters have it too good. IT'S TRUE WHETHER YOU LIKE IT OR NOT...
They don't have to build a
or
to scale properly, they can deal supplemental damage with their basic attacks, they can viably build lifesteal, and they melt turrets faster than Ap casters.
The only reason to take an AP caster over AD is to prevent armor stacking...
There's my rant, hope you enjoyed.