Not sure how someone says they, “think when applying ED it helps if you don’t apply for aid,” without having some basis for that. And it needs to be more than some full pay kids you know who had good admit results. It takes a great app package, every bit of it, down through LoR choices and interviews, to get an admit. Good chance you never saw their apps.
In the end, the focus should be on what makes a kid a solid match, in the colleges’ eyes. That’s a challenge to most kids, regardless of high school standing.