So my S24 was in a similar position this time last year. He is Bio with interests in Classics and Econ as well. Deferred by Yale, really liked WashU too, thought about ED2 at WashU, but ultimately decided to stick with RD. His reasoning was he wanted the RD shot at Yale and also was not 100% sure WashU would be his favorite offer.
Long story short, he didn’t get into Yale RD, did get into WashU RD along with some other great colleges. He ultimately visited WashU, Carleton, and Vassar post-offer, picked WashU, and is now having a great first year there.
OK, so was he guaranteed to get into WashU? No. Would you be? No. But he was very likely to have multiple good choices because he was a strong candidate who applied to a reasonable list of Reaches and Targets, and his Yale deferral indicated he could write a good application too.
That said, would it have hurt him if he applied ED2 to WashU? Turns out no, since he ended up there anyway. But would he always have wondered about Yale, and maybe other colleges? Possibly!
So it is entirely up to you, of course, and I don’t think there is a wrong answer. But I do think you should carefully consider the upside of having all your choices in front of you, of in fact being able to reflect on your choices when they are real offers and not just hypotheticals, before committing. And to me it does not really sound like you know it should be WashU. Maybe, but maybe not.