It is true that a higher percentage of ED applicants get admitted, and people sometimes get excited about that because they mistakenly think standards must be lower for ED. They are not.
The ED percentage is relatively high because it includes a cohort of top-tier students who are absolutely certain Rice is their first choice and are therefore comfortable binding themselves to the ED process. And on the other side of the coin, the RD percentage is relatively low because it includes more lower-caliber students who are happy to roll the dice on Rice as one of many simultaneous applications.
Bottom line, ED is a great option for many students but isn’t a way for people who’d be rejected RD to sneak in through the back door.