The folks I know who attempt to 'treat' themselves with substances generally just get worse. That's not a judgement, just an observation.

There are (illegal) substances that are highly effective for treating these issues, PTSD, etc. Psilocybin, ibogain, etc. Obviously when administered correctly, with therapy, etc.

It seems to me that cannabis users aren’t seeing the benefits of the aforementioned group. My experience of cannabis stoners is that it’s used to numb out and for escapism, which certainly aligns with what you’re saying.