I have BPD and PTSD as well. I didn't find my DBT group helpful, but the skills are(I had a therapist that basically printed out the workbook and gave it to me one handout a week). It wasn't at all "your coping skills are myths," but finding ways to manage impulses and destructive behaviors (like learning to recognize when vulnerabilities are higher than normal and I'm prone to doing things like drinking, disordered eating, and self harming so I can take steps to try and avoid those harmful coping skills/reactions and replace them with better ones).

Yeah, the group I was in sucked. It was like 50 minutes of going over the "homework" which was really more a couple members talking about their sister's sewing shyt or something stupid and 10 minutes of discombobulated lesson that wasn't even out of the actual DBT book.