your passwords are still as safe as your master password is
They’re as safe as your master password is…and as the encryption is. LastPass famously got hacked recently, and in the aftermath of that many users noticed that their vault was encrypted using very small numbers of rounds of PBKDF2. The recommended number of rounds had increased, but LastPass left the number actually used too low for some users, rather than automatically increasing it. Users of Bitwarden and any other password vault should ensure that their vault is using the strongest encryption available.
Self hosting wouldn’t really be a huge help there
Well, self-hosting makes you a smaller target. The most determined attackers are likely going to go after the biggest target, which is going to be a centralised service with thousands of users’ vaults. If you host it yourself they probably won’t even know it exists, so unless there’s reason for someone to be specifically targeting you (e.g. you’re a public figure), or you get hacked by some broad untargeted attack, you might be better off self-hosted from a purely security standpoint.
(That said, I still use centrally-hosted Bitwarden. The convenience is worth it to me.)