This is a linguistic problem. Just because the English language has limitations, it doesn't mean we should allow these limitations to dictate the extent to which we conceptualise things. Otherwise, we'll fall in the trap of shutting down our imagination because of this limited set of words we already have, AS IF languages couldnt evolve or we couldn't make up new words as we see fit.

So... although two distinct parts of tte human sense of identity are being alluded to here, both are referred to as "self". But if we cast the linguistic ambivalence aside, we can definitely see they're distinct, can't we? I mean, when we say narcissits lack a solid sense of self, what we mean is they don't feel confident trusting their own judgement without external input, validation, etc from the other people they see and talk to. If you dislike the word "self" in this context, you can propose something different. But terminological nitpicks aside, can you see what I mean?

"Self" as in "inflated sense of self-importance" simply refers to the ego (ie, that part of "you" which puts on a façade according to information collected over time about what others expect to see, sense, perceive etc coming from you in order to give you approval or disapproval in exchange), although I would guess the word "ego" isn't as universal as one might like in the field of Psychology because of its association, specifically, with Jungian theory(?) Which is why people use "self" there.