I do use Safari (mostly), and the keychain has worked well for me through the years. But Bitwarden (and other password managers) do plug in to Safari, just like they do with any other browser - and I can say it's working pretty well so far.
For me, Bitwarden actually offers a few advantages over Keychain, even if I stay with macOS:
- Bitwarden also can act as a TOTP client (two-factor codes, a la Google Authenticator or my old favorite OTP Auth). So it not only fills in my passwords, it also copies the two-factor numeric code automatically to the clipboard as soon as I log in.
- Bitwarden lets me access my secure notes on iOS and iPadOS. The fact that Keychain doesn't do that has always irritated me.
- Bitwarden gives me quick access to my passwords on the occasions I do use a different browser - or am at a different computer.
- Bitwarden has a command line tool! I can script it if I want to (I think Keychain can also do this, though).