Theoretically, introversion could be 100% genetic and, while that would mean that an introvert's identical twin would also be an introvert, both their parents could be extraverts.
I'm not saying that it isn't likely that, to the extent that personality is genetic, a person will be at least midly more likely to match one or both parents on one or more dimensions than to match neither. But "mildly more likely" doesn't mean there can't be a lot of non-matches.
Jung believed personality was inborn, and one of the things he pointed to in support of that notion was the fact that two children of the same parents could have such strikingly different personalities. To Jung, that indicated that it was unlikely that how a child was raised was the primary determinant of personality.
Decades of twin studies have been done since Jung wrote and, as it sounds like you already know, those studies strongly suggest that genes account for around half (or more) of the kinds of relatively stable personality dimensions measured by the MBTI and Big Five.
And the most counterintuitive conclusion that's been drawn from the cumulative data is that how your parents raise you has almost no influence on your basic temperament — e.g., whether you'll end up an INTJ. Identical twins raised in the same household are not significantly more alike (in terms of temperament) than identical twins raised in separate households.
For more, see this post.