It’s the same with Keychain...you need your face/finger/passcode to get into the phone, and then again to get into the passwords section or autofill. On a Mac, you need the master password twice to access passwords.
You may need the master password twice, but it is the same password. With a third party utility, you ideally would have two different passwords which is added protection.
AT MINIMUM, 1Password's security is no LESS than Keychain. To get to your data, a thief would have to access your computer/device (with a password/passcode) and then have access to your 1Password password.
If keychain is enough for you, by all means, keep using it, but for many of us, 1Password offers enough added value over Keychain to make it worth the cost.