More than $35 million has been stolen from over 150 victims since December — ‘nearly every victim’ was a LastPass user::Security experts believe some of the LastPass password vaults stolen during a security breach last year have now been cracked open following a string of cryptocurrency heists
Personally I don’t like to rely on anyone’s cloud services for mission critical applications like password storage, since they have a history of being discontinued without notice.
I do trust Mozilla a lot more than Google, though.
With Syncthing at least if the discovery servers go down you still have a local copy as well as off-site backups, and can easily migrate to some other sync solution as your password manager is not tied to your browser.
I would argue that email is similarly as critical, yet Selfhosting email is a bad idea practically and from a security standpoint. Your argument does not apply in general.