If proprietary app is better and more robust I am willing to try it and assess it myself.
But if the access to the combination of the two requires a separate 2FA (my Yubikey), then it is virtually separated. It is not just one password and you inside Bitwarden. One could argue otherwise, that having a 2FA app on the same phone as your password manager, is also not separate, if the same PIN/biometric gives access to that phone with the two apps on.
Do you use your Yubikey for 2FA or do you use it instead of a password?
If it’s the former then I guess it’s fine.