Hello sfwalter! 👋
Good question! If a website allows you to remove your old password after saving a passkey, and if you can use your passkey to sign in on all of your devices, then you can certainly remove the old password so that you're exclusively using your passkey.
We're still in early days for passkey adoption, most websites allow you to add a passkey as an additional login method but still allow you to use your username/password if needed. Some websites will allow you to remove the username/password entirely but others require that you keep both options. Part of the reason why many services leave passwords as a fallback option is because, for their website and apps, passkeys may not be supported across all devices and platforms yet.
I recommend that you continue to follow best practices and, if you do keep your passwords alongside your passkeys for certain websites, make sure that all of your passwords are strong and unique: Use the password generator to change and strengthen your passwords
-Dave