I'm not sure where you see that in this letter. What you see is gedolim have voiced there opinion that there is no validity to the heter.
Not sure what you mean "issue an all out machaah"
Many Roshei Yeshiva never would dream of getting involved in a heter eishes ish sheilah. They would hesitate to issue piskay halacha in oruch Chaim...
I have heard that while everyone knows that this "heter" didn't pass the smell test, the Roshei Yeshiva who are going to be mocheh required a serious posek to double verify that there is absolutely no limud zechus.
Here they received their final answer.
There is no defense that the "gedolim don't really know the metzius", etc