I think I've got to agree with this. Fi is my dominant function, so I act like an introvert. I don't need to apply my Fi to other people very much, so I'm not as social as I would be if it were Fe instead.In typology, I've come to define introversion and extroversion solely in terms of what a person's dominant function is. For example, I'm an extrovert because my lead function is Extroverted Intuition. Extroverted Intuition does not lead me to have many of the characteristics you've associated with extroversion, even on a lesser scale.
I use a lot of Ne and Te as well, though, so I'm not 100% introverted. I'd probably be more introverted if those functions weren't as developed.
I think the greatest drawback to being an extreme introvert would have to be social isolation. I also have an ENFP friend who used to oversocialize with tons of different people (to the point that she rarely spent a night at home) until she got really drained and exhausted.