Well you really missed the entire point of the show and summed up your ignorance of it pretty aptly.
It’s about way more than your surface observation. If you’ve been through addiction then it’s probably a show that will really resonate with you. The aim is not to watch adults pretend to be teens, it’s to watch people you can sympathize with, go through an incredibly difficult age and deal with a collection of problems that you’ve had before. If you’ve been through drug culture and made it out the otherside, you will recognize a lot of the characters as people you’ve known, or been.
You’re right that I haven’t watched it and know nothing about it, but I’m far from the only one since literally all I’ve heard about it is Sydney Sweeney’s tits are out in it.