I have (too many) siblings both older and younger and, at least in my family's experience, sometimes parents need to see this in action before realizing their behavior/parenting isn't right.

Take my family as an example, I've been years when i was a teenager complaining about how they treated me and my nearest sisters, which failed miserably as they didn't change and we ended up pretty fucked up mentally and one of them migrated and doesn't want to come back even to the same country. Some years later, I tried basically parenting my 2 youngest brothers, but respecting certain topics where my (religious) parents are a bit too sensitive. The first one has been the most peaceful teenage man in our family by far, and my parents noticed how i was approaching him (something similar to OP, but pre-shut in? Basically tried giving him an ally when possible). They changed their ways only after seeing their previous failures and a more healthy result.

... Tho it's worth nothing they have 1 child left to raise and most people doesn't have enough kids to have a full damn hero's journey about parenting lol