^ This.
The UI is slow and unresponsive, no matter what kind of rig you're running. Add to that unnecessary roadblocks and button pushes just to get a simple spell off, and it adds up to a whole lot of frustration.
The UI definitely needs some streamlining, which could have happened without splitting out all the spells (as was suggested, the AoE toggle could have been moved to a static widget and out of the casting process). But SE has other plans. Those who are up in arms about SE removing the toggle because they're speculating that it'll just give us two sets of the same spell may find out they're wrong (so, please, can we stop the angry finger pointing). As has been stated, they are looking at spells on a case-by-case basis. Maybe we shouldn't just be able to AoE everything. Maybe AoE's will come in a handful of special spells. Maybe they're restructuring the CON/THM spellbook. Maybe it'll be granted through Materia. We don't know yet.
But a change needed to happen and I'm hopeful that it'll be for the better.