I suppose I still don't understand how egocentrism is different, though.
Also, I don't want the thread to get derailed, because I do want to understand how cognitive functions relate to narcissism/egocentrism.
I don't deny that Ti isn't capable of narcissism. Without making an effort to use Ne, it's definitely possible for INTPs to dismiss valid points of view just because they don't fit into their framework. This is probably what's going on when we call something "stupid" that actually isn't.