If you confront an M2C promoter with Letter VII, the usual first response is disbelief. They have never been told about Letter VII and they won't believe you are giving them a legitimate document. That's why I pinned the link to the Joseph Smith papers at the top of my Letter VII blog.
When they discover that Letter VII was consistently and widely taught during Joseph Smith's lifetime (Letter VII was even published in New York City two days after the martyrdom), the M2C believers typically become defensive. They consult their M2C references such as BYU M2C Studies and Book of Mormon Central America. They call their thought-leaders.
Eventually, they will address their cognitive dissonance by claiming that the New York Cumorah was merely speculation on the part of Oliver Cowdery. It was his opinion, they will say. We have to trust the scholars and the intellectuals who are experts in this field. There's a scholarly consensus that Cumorah is in Mexico. Hence, there are two Cumorahs; i.e., M2C.
You can remind them of what President Benson said about the "mere opinion" rationalization, but they won't care because they don't like a lot of what President Benson taught.
President Benson: The learned may feel the prophet is only inspired when he agrees with them, otherwise the prophet is just giving his opinion—speaking as a man...
In the early days of this blog I focused on the M2C sophistry and semantic arguments because I wanted to point out the logical fallacies and sleight of hand the M2C intellectuals were using. Back then, I thought they were persuading people. Now I realize they were engaged purely in confirmation bias. Nobody would fall for their sophistry except those who wanted to.
You can go back and read some from 2015 to get an idea if you are concerned about some of the M2C arguments and how they sought to undermine the credibility and reliability of Joseph Smith and the Three Witnesses (and anyone else who taught the New York Cumorah).
The real problem of M2C, IMO, is how it acts as a gateway drug for sincere members of the Church to begin doubting the credibility and reliability of the prophets. When it is your own seminary, institute, and BYU teacher who is telling you the prophets are wrong about the New York Cumorah, it is far easier to believe they are wrong about other things.
And I think we all know where the intellectuals are leading us.