1) Very good way to show Christianity as another dimension of invisibility, along with "white" per Drabinski, hidden behind "Western." I think we should take that as a clue to uncover other interlocking dimensions of invisibility along with those two. "Western" also stands for "still-invisibly-ableist," "still-invisibly-hetero," "still-invisibly-anthropocentric," and so on. I don't include "still-invisibly-male" as that dimension of unthought default setting mode for philosophy is now becoming visible (to many people at least) thanks to the centuries of work by feminists.
2) When Schliesser notes the racism and genocidal calls of "the others" that you can find when you read outside the "Western" canon, that is to my mind a devastating counter to calls to "diversity." The call has to be to de-colonializing, de-racializing, de-ableizing ... philosophy, not just to broadening our sources. It's to change the way we do philosophy, to bring out the invisible dimensions which serve the social-structure-forming (or at least reinforcing and justifying) as well as epistemic, moral, and aesthetic functions of philosophy.
3) The still-invisibly-Christian aspect allowing "Western" to be used as it is didn't become awkward after slavery and colonialism the way it did after Auschwitz, perhaps because of the long term nature and intricate workings of slavery and colonialism meant the entire society, religious organizations and doctrines included, were so permeated by and so involved in the reinforcement and justification of those power relations that can't we see that involvement in the past, let alone see it now in our current society, still structured as it is by the succeeding permutations of the racism and exploitation that were slavery and colonialism. The documentary evidence presented in the case of the Jesuits at Georgetown show just how direct that involvement could be; the real challenges lie in showing the more indirect cases -- as well as continuing to unearth other direct ones.