YYA, thanks for a long exposition on MM. Your explanation of Biur is new to me, but sounds plausible, and I am aware of the rest. I think your reasoning shows where we look at things differently: you presume that the only possible type of interaction of a frumer Yid with modernity is “kiruv” – that is we just need to show “them” how wrong they are. Hadash asur min haTorah, to quote the MM antagonist. Others, that I think include MM, R Hirsh, R Soloveitchik and l’havdil AAQ, think that we need to address the changing world – as did all generations of Jews and other tzadikim. Adam worked the fields instead of remembering the life in gan eden; Noah built the ark and took care of the animals instead of writing memoirs about the destroyed world; R Yohanan b Zakkai predserved what he could instead of ignoring presence of Romans. As R Soloveitchik writes, if we claim to have Hashem’s Truth about Life, we should not be hiding in caves. (I am ignoring here cheap ideas of Reform and such as “adaptation” to modernity, I am talking of true Torah response).
So, from this POV, German Jews were on the way to modernity one way or another. Hasam Sofer saved some in Hungary, but, to my knowledge, had not much effect on his native Frankfurt. Only R Hirsh did. So, my imperfect understanding is that MM tried to find compatibility of his Jewish views and his views of modernity. I am in no way saying that he had success, I am saying that he made an honest effort. And he was in a good position for the effort – both solid Jewish background, personal integrity, and advanced understanding of modernity (Kant was the major figure of Enlightment and he had great respect for MM). Besht indeed was born earlier – but he did not have direct contact with modernity. Even R Salanter, way later, said at some point that he can not do much for Litvishe Jews as they are sliding down the slope, and he sees more hope in talking with a French professor who is at the bottom but is at least stationary.