Okay, I guess from a natural selection point of view, it wasn't THAT unfounded, but you can't really state that extroversion is strength and introversion weakness as it is a subjective opinion (even if it may be true). Since it is subjective, you can pretty much dismiss it by saying the opposite unless you have definitive proof that your view is correct.
You can't fully use natural selection 100% as a measurement of strength with humans anyways, as humans have intelligence (unless that IS a form of natural selection, then I guess this argument is invalid). I find it very hard to believe that humans got to where we are now on caveman social instinct alone, think about it, if humans had no intelligence/ just instinct, I think it would be pretty difficult to beat any animals to survive without becoming prey (try fighting a lion bare handed and try to prove me wrong).
Due to intelligence being in EVERYONE (introverts and extroverts) many introverts will be able to use their intelligence to mate and survive (don't ask me how, ask the intelligent introverts)!
Besides, evolution is just a theory, meaning all of this natural selection stuff could be wrong anyways (unlikely, but possible). You also said that the weak introverts die out- so does that mean the the strong introverts mate and survive, or all introverts are gone forever?
That would be pretty hard to do anyways, to wipe out all introverts, as humans will continue to mate, and statistically speaking many introverts would be born from the so called "strong" extroverts.
It's funny, the process you talked about in your post pretty much theorized an involuntary genocide of introverts (almost like what the Nazis did to achieve a "perfect" race). I'm sure you didn't mean it like that, and natural selection isn't technically genocide, but they do sound pretty similar.
In short: if you are right, total extinction of introverts would probably take millions of years, so it's none of our concern!