(A) Martin Luther is the best known of them
The modification issue is only one aspect of the structure. Perhaps A may pass that. But the problem with A is the built - in redundancy of the phrase ‘of them’
‘
Of them’ is duplicating ‘
of the people’. Flip the sentence and you will see the effect of it
Martin Luther is the best known ‘
of them, of the people’ who brought about the Reformation, the religious revolution that grew out of objections to the doctrines of the medieval church,
In B, you find no such redundancy
B) The best known is Martin Luther of the people who brought about the Reformation, the religious revolution that grew out of objections to the doctrines of the medieval church
Although this is a little bit of poetic writing, still the classic sentence is:
Martin Luther is the best known of the people who brought about the Reformation, the religious revolution that grew out of objections to the doctrines of the medieval church
The difference between the Soviet Union case and the Martin Luther Case is that, in the former, the problem of was one of an unequal comparison of a country with a border, while in the latter, the comparison has been correctly made between "
of the people and Martin Luther." , a human with another human.
Both cases are vastly different in syntax