Ugh. Please let me explain, as briefly as I can.
There are three levels of consideration here:
If you understand the legal system and history the three are indelibly tied together in Western Democracies; examples Bernie Madoff and Ariel Castro, both of whom received laughable symbolic sentences.
My quibble here is definitional (not semantics, as some keep saying). A slave is held as property: the lack agency, freedom of choice, freedom of movement and the prerogatives of self reliance. This matters: it's how we define slave states and empires throughout history. When we set to work ending modern slavery and human trafficking these are the qualities we are looking to eradicate.
The victims in this case possessed none of those qualities then or now. They have made overtures about being "forced," but in what measure?
And yes, I do generally think we get too wound up about certain things, statutory rape among them. I am not advocating for sexual relationships with minors. However, rape and statutory rape are not necessarily as closely related as our language implies (this is intentional). When I hear a woman has been raped my heart breaks - whether date rape, violent stranger rape, non-consensual contact while unconscious, etc. these all count as rape and deserve to be taken seriously.
Statutory rape on the other hand has nothing to do with rape and everything to do with exploitation. We can say all we like that teenagers "can't consent," but they do. They do all the time. I did. My friends did. Both make and female. We consented whether we were mature enough or not - and many of us were mature enough. I first had sex at 14. I was 28 when I became a father and have contracted one STI in my life. Obviously it wasn't such a massive responsibility that I and my partners couldn't handle it.
Now, you are correct that grandiose claims are generally irrelevant at the legal level. They will be at worst an irritant dismissed or disallowed by a judge.
But, juries and even judges on the sentencing side are politically sensitive to Public Relations. If I'm on a jury and believe I'm about to hear a case about "sex slavery" and what I get is a case that has nothing to do with slavery or even rape - I may just find myself less than inclined to take the plaintiffs and their complaints seriously. It's a simple fact that juries make decisions based on who and what they like. It's never a sound strategy to overstate a case.
Morally however, and this is my wheelhouse, the claim of slavery is abhorrent. I've read the background - Epstein has already been through one criminal prosecution - none of what he did or what he is accused of qualifies remotely with the keeping of slaves. But reddit, multiple news outlets and a huge number of commenters here and elsewhere seem to think making this about sex slavery is reasonable or justified.
Read the accounts of these young women - dozens of them - from the criminal proceeding: they entered willingly - albeit grossed out; went only as far as they were willing - enticed by the promise of more money; left when it was over - and a huge number came back to do it again. For more money. That's not slavery. It's prostitution. Committed by 16 and 17 year old girls. My wife and her friends all say the knew what they were doing at that age - even if their decision making wasn't great, they knew what they were doing.
The only thing that I don't understand is what these four women are suing the federal government for.