I think that the danger of a password manager data breach is emphasized too much when considering how these companies are securing people’s data. If I remember correctly, 1Password has even stated that their threat model starts at having their servers compromised, which is why they, and other password managers have designed their systems in a way that the impact of a possible data breach wouldn’t matter that much.
In addition to end-to-end encryption and strong KDFs, 1Password has the secret key mechanism, while Bitwarden has achieved something similar with its multifactor encryption. In both cases, a data breach wouldn’t have any real impact on the user, as the attackers wouldn’t be able to decrypt the exposed data. However, it seems that Proton hasn’t implemented anything similar and their current security model needs an update. Still, even in their case, a sufficiently strong master password would protect your data even in a case of data breach.