The system deserves to break down if you can pressure people to settle claims against other people who you have no responsibility for then it shouldn't stand up in court.
What consideration has he given to the contract?
Imagine if a class action law suit was settled with a conglomerate for e.g. knowingly selling dangerously carcinogenic products and the agreement forbade the claimants from bringing similar claims against any other company that was a possible target of takeover by the conglomerate or an actual acquisition.
The lawyers in that circumstance would be wrong to agree to such a clause but such a clause would be perverse.
The Epstein-Giuffre agreement is a perverse document that did precisely what it claims not to do, it concealed and shielded criminality by paying off one of the victims and witnesses. VG had some part to play in that too, by accepting such a paltry sum for her silence when the right thing to do was not to go away quietly.
I don’t think she’s pleading (or there is anything to suggest) that she was subject to duress or undue influence around the formation of the contract and would have been legally represented and advised at that time (and previously).
The consideration came from Epstein, which subject to enforceability of the contract more widely by a third party, will be adequate both in law and sum for the agreement to be valid.
In the tobacco scenario you paint, the claimant should be precluded from bringing any other claims against third parties imo. That is the risk they take when they freely enter into the agreement. (That clause could be there for perfectly legitimate commercial reasons btw, maybe a pan-tobacco industry code).
Parties enter into such agreements to remove doubt to and on both sides. To give certainty in order that the parties can move forward from the litigation, as long as the terms are adhered to. It’s the same principle thst underpins limitation periods: certainty.
(btw, based on the double-counting damages principle not sure they’d be able to bring any further claims against any other corporations in any event.)
If Guiffre had wanted that clause removing or amending as part of the discussions around the contract, then she was at liberty to raise that - it then would have been a matter for Epstein to consider how important it was to him in that form. Presumably those discussions never took place, or they did and Guiffre, being legally represented and advised, decided to sign anyway and accept the $500,000.
If the lawyers, as you suggest, were ‘wrong’ to agree to that clause, and they were professionally negligent,then Guiffre may very well have a claim for damages again them, but not Andrew imo.
Your last sentence supports pretty much all of the above.