In my experience - I'm early 20s, diagnosed with BPD & autism.
I was under child services until 19, which I actually did have a good experience with, but after I aged out of those I kinda just got left to it? There was no continuity or any real support offered beyond that. I basically jumped from service to service after that because none of them wanted anything to do with me. Wellbeing services wouldn't touch anyone with a PD, specialist services had a wait list of 18+ months, GP wouldn't do anything beyond offer me SSRIs I didn't want. The one time a doctor actually referred me to be seen by the adult mental health team, I pretty much got told to do one because I'd worn makeup to the appointment.
But then I moved, and my experience since has honestly been the exact opposite. I've been listened to, taken seriously, and my care has been coordinated well. I actually feel supported and cared about, which has been really nice. My primary point of contact has really gone above and beyond for me, which has truly made a difference.
So overall, I think it definitely varies by area, condition, diagnosis, and even by practitioners themselves. It's definitely a coin toss, and the system overall is broken and underfunded asf