To Jonathan Chait's point, I put AOC's DNC address into readability formulas to see what the score would be:

It's definitely college graduate level language, for the most part.

But what happens if you put in Michelle Obama's speech?

So AOC's language was definitely more geared towards college graduate-language whereas Michelle Obama's speech used language that was more accessible. What about Bernie Sanders?

Bernie Sanders is slightly higher than Michelle Obama but below AOC

Readability formulas have their critics but I used a bunch of different ones and they generally do give you a clue about what level of education a text is aimed at. So broadly speaking, @jonathanchait is right. But Michelle Obama would've been a better comparison for alternative.

The important thing about these formulas is they don't show you what is "better" -- that is for you to decide based on audience, what you're trying to convey, etc. But they do show accessibility. Obama's speech was the most accessible, then Sanders, then AOC.