Maybe you have a different professor in mind. In my law classes, I have heard some speculation as to the exact meaning toward the 14 amendment, but I have never heard condemnation of them.
Both of your points are immaterial to what I said. He said it was much discussed in academic circles.
But in order for it to be "much discussed", there has to be two sides, presumably one that agrees the amendments were not passed legally.
But tell me now law professor, what does the law think of contracts made under duress?
Contracts made under duress are not valid. But saying agree with this amendment or you will not be readmitted to the Union is not duress. Just a few years earlier those same folks said screw the constitution and all the promises we made.
Duress would be “agree with this or we'll hang your treasonous ass”. That’s duress. ;~))