For sure the rise of the Reformation made the need for an indisputable (per Rome) canon, but it certainly was not Luther who made Scripture the focus of theological argument, and if that was more the case with Rome, i think it would have resulted in a much earlier final infallible definition of the canon.
As it was, there was a good degree of historical “consensus” on each side of the canon dispute, and Luther’s opposition to Purgatory and position of the supremacy of Scripture (not to the exclusion of tradition) necessitated 2 Mac. to at least be part of the Scriptures,
As for Revelation vs The Shepard of Hermas, the character of writings which were Scripture, like human character, became more manifest in time, and by the fifth century the East, with a few exceptions, had come to accept the Book of Revelation as canonical.
Once Luther had repudiated Rome and the Councils as overriding authorities, what was left to him as the basis of his theories but Scripture? To be sure, the radicals dispensed even with Scripture, thinking that they Holy Ghost spoke directly to them. but Luther was too much of a traditionalist to do that. Plus he knew so little Greek that he did not know how defective Erasmus’s work was, because his sources were inferior.