You guys should get in to MBTI, The way the functions are described there are a better explanation for personality types and it also goes further in depth. So, if you believe in MBTI, Introversion is a spectrum, not an absolute. For example, FE (Extroverted feeling) is the most social function because it is a person's tendency (and ability) to focus on the emotional expressions of others rather than their own emotional state. So, an ISFJ (Leading with introverted sensing with extroverted feeling in the auxiliary) MIGHT be more sociable (not necessarily introverted) than an ENTP, and even ENFP, because ENTPs and ENFPs lead with Extroverted Intuition, the most introverted extroverted function. Introversion and Extroversion aren't explanations for sociability, think of it more as various factors in your personality that impact sociability rather than define it.
(Most important) Introverts are less social than extroverts because their lead function (whether perceiving or judging) is aimed inward
(2nd most important) People that perceive with intuition are less social than sensors because intuition involves ideation more than sensory experience, so they must retreat within themselves to evaluate the ideas that have encountered either from within themselves (introversion) or from without (extroversion)
(3rd most important) Thinkers are less social than feelers because they value logic above all, and their judging functions are based on impersonal systems that value logic over how actions will affect others. Again, this is the 3rd most important for a reason. Introverted thinking is likely the most introverted function PERIOD, but again, the first two letters of your type are much more important than the last in determining your sociability
(least important) Perceivers are less social because they turn their perceiving function to the outside world. So they interact less with the actual world (and thus people) because they don't have agendas as strong as Judgers do. Again, this is the least important letter in determining your sociability