“These women should either learn the sugyos of tevila b’iyun or not make these halachic determinations.”
Agreed. And that is precisely what happens at Yeshivat Maharat and Nishmat.
“I have come across a few stories (first and second hand) of Mikva Women making terrible halachic mistakes with potentially grave consequences.”
And that is why we need institutions like Yeshivat Maharat and Nishmat.