I think people rely on comfortableness/abilities to extravert too much when deciding their I vs E type.
I'm at the point in my life now, after having spent a year traveling to a new place every single week, including in Africa, living in very unfamiliar homes (both culture-wise and literally not knowing the people) and all my life experience through joining new sports teams/clubs at school that I can extravert more naturally/comfortably than a lot of extraverts. I enjoy it. It does give me energy when I choose to do so.
Yet, my natural inclination is to stay at home and go on the internet/read/do my own thing for a week without even thinking to go out an socialize sometimes. I'm just most attracted to being alone (assuming I socialize enough to keep me mentally healthy). I resent people who try to make me socialize more than I feel like doing; I find my alone-time to be very valuable and am aware that at 21 years old, I won't always have this luxury to be so independent with my time, so I take it now (before I have a career/family, etc.)