Dartmouth is about 67%; Brown about 70%; and Harvard, about 32% undergrad. I don’t think that means that you don’t get an outstanding undergraduate education at Harvard, but I think it does mean that Dartmouth and Brown are more undergrad-focused, overall, than Harvard is.
In some ways, I actually think the presence of grad students in classes can rub off positively on the undergrads sharing that space. But if we’re talking about elite universities that are most like LACs, I think the most obvious stat is % of all students who are undergrads.
And in that regard, Dartmouth, Brown, Princeton, and Cornell are all at least 65% undergrad. The other Ivies and Stanford/MIT/Chicago are all under 50%.