The only true secure master password is one you do not use elsewhere, and one you can remember. Not sure I know the diff between a password and a passphrase they are both just secrets known only to you. Maybe one has spaces? NEWays…
Having it only on a yubi that you don’t remember puts you at risk of loosing they key and like biometrics it can be compelled by law. The password only in your head cannot be compelled, at least in many places. A good stick will compel about anything. 
Using a longer password has high entropy especially with unknown dictionary words. You can literally make most countries cringe at the cost of cracking it given proper Argon2 and the right params.