Would not Half-Elf (High) work better for this, given the innate CHA bonus
But then you would lose the ability to wear Light and Medium Armor which is a big part of the defensive build.
In 5E if you are proficient in armor you can wear it while spellcasting.
How often did you find yourself getting hit by sleep?
Not gonna lie, that is a weakness with the build - but one shared by Tieflings, Githyanki, Humans, and Halflings as well. It doesn't happen often but it can happen.
The bigger problem that this attempts to solve is the Low-AC mage getting steamrolled by the enemy AI which targets either mages or lowest AC individuals. Sleep is less of a problem than getting downed in round 1 or 2 and then being a liability for the rest of the encounter while the AI continually re-targets you and knocks you out. I have seen it, so many times. Its like you may as well not even bring a mage.
If you can rock 19AC - you just won't get targeted as much and they will connect much less often. You also save a 1st level spell slot.
