But if Meta wanted to hire you and had perfect information, it sounds like they'd discover they needed to offer you salaries in the $350-400k range? That sounds like it might be good for you.

The story you seem to have told is they just wasted time low-balling you because they didn't have enough information to offer a competitive salary. You weren't ever going to settle for $250k, they didn't have enough leverage and they lacked the information to identify that. I'm not sure how you're seeing this story as one where more information to Meta leads to them offering you a lower salary. It seems like you'd have rejected them regardless unless they went higher.

All the employers knowing that you'd have "taken the job even if they offered $200K" seems to be completely useless to them. They're locked in an auction and the market price for your time is nowhere near $200k.