Oh. I didn't know there was a "middle grade"; I just assumed it meant "middle school".
So, I'm reading the annotations, and this popped out at me:
Only Elantrians can draw Aons in the air, so someone taken by the Shaod must have developed the writing system. That is part of what makes writing a noble art in Arelon--drawing the Aons would have been associated with Elantrians. Most likely, the early Elantrians (who probably didn't even have Elantris back then) would have had to learn the Aons by trial and error, finding what each one did, and associating its meaning and sound with its effect. The language didn't develop, but was instead 'discovered.'
Emphasis mine. So, the Shaod did
not begin with Elantris. Why, then, did the chasm break the Shaod? My best guess is that the giant Rao was, like all other post-Reod Aons, completely non-functional, and the Shaod wasn't broken, it just returned to the way it used to work before Elantris. Like the Reod-Elantrians' too-weak Aons, perhaps the Dor just couldn't get enough power through the divide to accomplish its purposes without a little help.
It must have taken a serious genius, like a Newton or an Einstein, to figure out that building Elantris would so enhance those taken by the Shaod.