“Doubting his authenticity without being in proximity of the context is a whole different story.”
Then it’s a whole other story, but it’s still related. People might be questioning him for his track record on other things as well and this was just the straw that broke the camel’s back. Had this been Shmuel Kamenetsky, people would probably not be asking these types of questions. Given your defensiveness about R Mirvis, I think you clearly realize this as well.
“There can be schisms that both sides are fully within halachic bounds.”
Yes, there can be, but that doesn’t mean all schisms are within halachic bounds. Probably not even most. Schisms based on one side ignoring the halacha are a lot more relevant than subtle differences in derech halimud between one yeshiva and another.
“We have a bunch of systems (Omer muttar. Shogeg. Tinok shenishba. Taus.) that allow us to remain in close contact.”
Irrelevant. We’re talking about whether or not actions are mutar, not whether or not the person would be chayev and if so by how much. Someone might be a tinok shenisba and be patur, but it doesn’t mean their actions are mutar.
“My insistence on using the term ‘we just don’t go into churches’ is only intend to make the matter more serious not less.”
How do you figure? Saying, “it is assur to enter churches” certainly sounds a lot stronger/more serious than “we just don’t do it.”