In any lawsuit mill of this size, they have to know that they have false positives in the people they accuse, and that some innocent people will settle rather than fighting it.
That probably opens up some avenues of recourse. First, the wrongly accused could almost certainly go class action, since not only are they obviously a class, but the companies in question have declared that they are.
Secondly, the lawyers filing the suits are expected to act in good faith. I don't know if it's ever been tested, the idea of "I'm pretty sure 95% of these people have committed the tort." Certainly, I'd pitch some cash into a pool to go after the lawyers and law firms themselves on the principle that they are knowingly filing claims against innocent people. Simple statistics say it has to be knowingly, right?
Finally, hopefully someone will set up a resource where those who have been threatened can band together and pool funds for defense. This is a classic divide-and-conquer maneuver, and if a thousand people each pitch in $1000, that's real money for defense. And, again, the law firms are asking that the cases be combined, so this plan works fine.
* IANAL, etc, etc.