If you mean the value of Facebook, of course it's worth more. But nobody would give them the entire value of Facebook, not even close. They settled because, apparently, their lawyers thought it was the best deal they were going to get. Otherwise why settle in the first place?
They're not trying to get the settlement undone because they didn't like the settlement itself. They're just claiming that Facebook lied about how much money exactly they were getting as part of the settlement.
"No sane lawyer is going to advise them to settle for a fraction of what they might actually have a legal right to. Too much money is on the table."
Well first of all they did settle, originally. And by the way, they refused to pay their first lawyers (who did the settling) for 2 years. Recently, a judge ordered them to pay their lawyers.
"The crux of the argument (for me personally) is whether or not these guys hired Zuckerberg to build the original version of what became Facebook."
They did hire Zuckerberg to build their site. This is not contested. I'm pretty sure it's also uncontested that Zuckerberg didn't copy any of their code or anything. How similar the two ideas are is something that's pretty hard to say, though.