You are, by extension, saying that PFS is not as big a deal as you are making it. Do you have anything to back this up that Signal et al aren't aware of? Would you like to argue Delta Chat should stop arguing in favor of it too?

Seems super dangerous to assume security due to ignorance of harm, but okay, I guess, we can play "look for why".

With DeltaChat, you can get a private key just by accessing a file on a desktop client. Or a backup file . Then you can pass that onto a compromised server and restore chat history that wasn't present on the client or backup file.