Yes. 750,000+ people per Representative is ridiculous.
And an unwieldy body of 6,563 Representatives wouldn't be?
There's a middle ground. 1000-1500 members should work fine, given a strong hierarchical leadership and committee system (which the US Congress already has).
What's the point though? I get the argument for the Wyoming Rule to minimize population variance between districts, but after that, it seems like you're just adding representatives for the sake of it. I don't think there's anything more democratic or effective about having a rep for every 300,000 instead of every 600,000 people.
Large districts lower the quality of democracy. Representatives can't possibly represent meaningful communities, and constituents can't hope to have meaningful interactions with representatives. The nature of campaigns change as well, as larger districts means that campaigns are more reliant on ads (and therefore on big money) than on grassroots presence and word-of-mouth. All around, a lot of the pathologies of modern US politics are, if not a product of, at least made considerably worse by large districts.
That may be, but these issues would still apply to any constituency of over 100k people. 250k-300k person districts, like you propose, would still be too big for meaningful constituent interactions and relevant community representation. However, constituencies of just 100k in the United States would produce an unacceptably large congress, leading me to think a sub-1,000 member congress is the way to go.