[dublinben]

OP already mentioned that the UX on mobile was really bad.

A real password manager (like Bitwarden) would be integrated into the mobile OS, and automatically prompt to fill passwords. It also doesn't provide any functionality to generate secure, unique passwords for each site, so it encourages insecure reuse of passwords. Further, it can't notify the user when a password has been compromised and should be changed.

Different people have different threat models, and improving usability of good tools can improve security more than perfect tools would.