For what it’s worth, I think @sahmkc is more right than not, and @menloparkmom the opposite on this issue. (And, by the way, divergent opinions are usually expressed on CC. Just not always in a two-hour window on Suinday night.)
ED/merit policies and strategies differ widely from college to college. The standard folklore about not applying ED if you want merit aid is worth paying attention to, because there’s a lot of experience baked into it. But it’s not an absolute truth across the board. If you care about a specific institution, go deeper than that. If you are in the OP’s position, it behooves you to investigate the specific college carefully rather than relying on general bromides and anecdotes about other institutions. Or even anecdotes about the same institution that are a few years old, since these practices are definitely subject to change.
Yes, it’s true that in many/probably most cases, applying ED is inconsistent with getting the best merit aid, or any merit aid at all. Unless, that is, the college has automatic or first-come-first-served objective merit standards, which some colleges do have.
No, it’s not true that, as @menloparkmom put it, in an ED situation the college holds all the cards. The college holds more cards than it would in most RD situations . . . maybe. (What happens in RD if you don’t have a better financial option that the kid and family feel good about? That can happen, too.) A kid accepted ED can decline the admission on financial grounds. If he or she does that, that’s it for the college, there’s no RD round, but it’s absolutely possible to say to an ED college, “This is my first choice, I desperately want to come here, but it won’t work for my parents and it won’t be fair to my siblings unless I can get the price down by $X.” If you are prepared to walk on that basis, that’s a lot of negotiating leverage.
And more traditional leverage may come if you have applied to and been accepted by EA or rolling admissions colleges. Not all of them make merit offers by December, but some do. It may very well be the case that, say, an in-state directional public with rolling admissions and automatic merit could provide an excellent stalking-horse for negotiation with an expensive private like GW. "My family is willing to pay more for your wonderful college than we would pay East Podunk State, but it can’t be more than twice as much . . . "
As a matter of admissions strategy, it’s not obvious at all that colleges can ignore ED applicants with their merit money. Any college would love to have high-stats students who really love that college applying ED. If concerns about possible merit awards (discounts) are stopping students like that from applying ED, the colleges ought to be going all out to assuage those concerns.