Agreed. My understanding of introversion is that it takes energy to socialize and an introverted person gains energy with more time alone for things like introspection. That can be independent of social skills and degree of enjoyment from socializing.

Extroverts find socializing energizing. And can find alone time draining.

Of course most people aren't fully in one or the other and some circumstances may change things.

Shyness is more the classification for social wariness which might be coupled with a perception or skills deficit in addition to the negative beliefs or feelings around socializing.

I'm definitely more on the introvert end of things. But after a long time of solitude I get a hankering for socialization and feel energized by interacting with friends and family, up to a certain duration. And then a while after that I can feel overwhelmed or drained and then need to find alone time for myself to recharge.