You really can’t directly compare yield rates of college with EA vs. those with ED. An EA college can likely bump up its yield several points by switching completely to ED. If Chicago only had ED, it would easily pass Penn.
For that matter, you also can’t directly compare an unrestricted EA system (MIT, CalTech, UChicago) with the Single Choice EA systems practiced by HYPS. I think that HYPS would lose a few yield percentage points if they went to unrestricted EA.
It will be interesting to see what happens to Chicago’s yield next year with the addition of ED1/ED2.