The supposed "draining" of introverts sounds like a cold reading technique or something you'd read in a horoscope. It applies to nearly everyone to some degree.
Enjoy socialising but after a party you're glad to put your feet up and read a book? Get slight anxiety making small talk with strangers, to the point where you feel bad if you do it for more than six hours? Don't want to hang out with your boss at the mandatory company event on the weekend when you could be with your husband and kids? Congratulations, you're A) perfectly normal and B) an introvert, sort of, if you squint!
The problem is not that I don't get what it's like to feel drained, it's that I'm pretty sure everyone I hang out with except for literally one single person feels drained by social interaction at some point.