I think like a lot of things its not a question of one or the other its a spectrum to varying degrees, some people might need less or more alone time than others and some people need to be around others more. But I also think this can fluctuate slightly throughout your lifetime.
In my previous experiences I have found so******ing stressful and unfulfilling especially when I have been sat silent as part of an animated conversation between others and I have been worrying about what I am going to say and not really being interested in what is being discussed and worried about being mocked. I would all the time find myself craving to be alone . I would feel so drained afterwards from all the worry and couldn't wait to get home so I could relax (recharge) and do activities I had an interest in, by myself.
I would sometimes take holidays off work to get away from the stress of being social at work. I would not tell anyone outside of work I was off and just spend the day alone and then pretend when I got back to my work colleagues I had done something cool. That's how extreme my "introversion" was at times.
Lately though and looking back on it building up over the last couple of years or so I have become more confident socially and found a group of friends I am more comfortable around, share similar interests with and at the moment I have a girlfriend that I have become comfortable around as well.
I find myself now still sometimes craving my alone time but its becoming fewer and farer between as I now seem to find myself easily bored when I am alone and the solitary activities I once craved and loved so much like tv, books and gaming are now often unfulfilling to me, They quickly bore me and I find myself wanting to be out doing stuff with my friends or spending time with my girlfriend more often than before.
I believe it is true that you can get a confident or unconfident Introvert and the same polar extremes for an extroverted person but for me my need for solitude to recharge and need for companionship for fulfilment has tipped on the scale solely due to my situation and control over my anxieties.
I would say that I have gone from an unconfident introvert sliding to a more confident extrovert in recent years.