I'll agree with that, I mean even though Ivy isn't a top batman villain any one in the top ten of his rogues gallery is pretty widely known and marketable. It's not until you get to villains like Calendar Man and Great White that it's kind of ridiculous.
But I can see low ES on smaller characters that aren't as huge. Like as much as I give Aquaman love, and I do guys I think he's one of the most misunderstood characters, I can see a much lower ES on him.
But Batman and his top villains/family, Superman and Family, Wonder Woman, Flash, Green lantern, forget it they're is going to be a larger number because they can market them.