Sam: 1) The Nachalas Shivah is irrelevent to the prenup argument. Even Rav Asher Weiss, who supports the prenup for other reasons, admits as much. Rav Weiss writes about the Nachalas Shivah as thus:
???”? ??? ?? ???? ???”? ????? ?????? ????? ?? ????? ?????? ???? ?????? ?? ???? ???? ?????? ????????, ??? ?????? ???? ?? ???? ???? ?? ????, ??”? ??? ??? ???? ?????? ????.?
“In my humble opinion this is not related to our case for it seems that this enactment’s fundamental purpose is really to guarantee the well-being of the woman and the distribution to her of her food, and not as a medium to force the husband to divorce his wife, and if so there is no proof to our case.”
And she can’t demand what “she deserves”. Mezonos is based on the cost of basic living expenses for anyone in that locality. Furthermore, the BDA prenup kicks in the so-called “mezonos” even in cases where there is no halachic obligation to give a Get and cases where he has no halachic obligations to give her any mezonos. (See previous comment on the Rama.)
2) $Over $50,000 per year, for one person, is most certainly not “about the same as what is considered a median middle-class income”. The only way you get there is if you count a two-parent income, in which case a) she is already keeping her own income, per the prenup, even though halachicly if he gives her mezonos then he gets to keep all her income and b) if $50,000 after-tax for one person is what you call a “median middle-class income” then a two parent family with four children would need something like $200,000 pre-tax to be middle class. This is an absurd argument for both these reasons and this is blatantly obvious. It is a penalty not mezonos.
Matan: Rabbi Schwatz is MO. The RCA doesn’t disallow members from being mesader without the prenup. And despite the rhetoric, the very clear majority of MO chasanim don’t sign it. In the non-MO world virtually no one signs this prenup. And according to the Pew Research study from less than two years ago, 81% of American Orthodox Jews age 30 and younger are Chareidim.