since we're effectively saying that they Aren't praying to the same one G-d that we are, even if they strongly believe that they are- just in Ways that we don't think are applicable.

Are we, though? Who says we're talking about them at all? The original context was about idolaters; who says it's saying ethical monotheism other than ours doesn't count? Maybe the rise and spread of Christianity and Islam is covered by the second paragraph.