My knowledge is a slightly bit larger on this issue thanks to JSTOR but my feeling that the issue is not so black and white comes from my experience of living in Croatia. There the efforts to purify the language of Serbianisms (and anglicisms and Germanisms etc) was about changing how the whole people spoke. It was also about the elite (new and rebranded old) displaying their superiority. I doubt very much that the Katherevousa movement was free of that tension between populism and elitism.
Of course Katherevousa was part of a modern nationalist movement but Attic revivals lend themselves to a nostalgia for past glories of Greece and that is going to be political in at least some sense. Plethon (who died only a few years before the fall of Constantinople so as late Roman revivals it was pretty late) did not simply write in Attic. He also stressed a Hellenic as opposed Roman identity and advocated transforming Morea along lines that echoed the aims of Agis and Cleomenes.