Using a KDF for stateless passwords is a interesting concept. It isn’t prefect tho. What if you want multiple passwords for one site, lack of any 2FA, KDF has to be somewhat fast (bcrypt or scrypt what takes under a second) & once your master password gets leaked your screwed (compared to cloud stored passwords with 2FA, key rotation etc)
Realistically stateless password managers suffer from the same attacks cloud based ones do, MITM attacks. If the client is open to being tampered with, your keys can always get leaked.