Yeah, I have looked at them, and you're right - I should be careful not to describe this as solving an unsolved problem, because it isn't one. DeltaChat, SimpleX, Session and Jami all exist and several go further than I do on PII. Session and Jami in particular don't need an email, which is more than I can say - I traded that bit of privacy for account recovery, deliberately, but it does mean they're ahead of me on pure "zero identifiers."
So I won't pretend I filled a gap nobody else had. Honest version: I went down the rabbit hole, didn't love how the free mainstream options handle data, and built my own partly to learn and partly because I wanted it to exist. Where I'd say it differs is the no-install browser/PWA approach and post-quantum from the start - not "nobody else does private messaging."
The "scratch your own itch even if it's been done" point is basically how I'd defend it too. I'd rather be honest that it's one more option in a crowded field than oversell it as something new. Appreciate you listing those - genuinely useful for me to study how they each handle the no-PII side.