Regarding Catholic beliefs on this matter...I will read what you have provided at your link, as I have time, and see what I think....thanks for providing it, for me...
Please be aware Unam Sanctam has been "explained" away over the ears to say essentially "it doesn't mean what you think it means." IOW contemporary Catholic teaching is that "salvation" is available to "non-Catholics under varying conditions. While it is not possible to deny "infallible teaching", it is possible to redefine it.
Thus the facetious, but essentially true statement, "There is no Catholic teaching which is so clear it cannot be denied, modified, or reinterpreted as required."