Yeah, that's fair. I think FileZilla shows who signed the cert, but yeah it still gives that pop-up asking the user to decide and I haven't checked whether they

Yeah, that's fair. I think FileZilla shows who signed the cert, but yeah it still gives that pop-up asking the user to decide and I haven't checked whether they verify that signer against the system CA list. Either way, that's as canon as FTP clients get and since they don't have it, indeed it's mostly opportunistic encryption. (Not that relying on the CA system rather than TOFU'ing or sharing a fingerprint is without problems of its own, but that's a discussion for another thread.)