I agree with you. A passphrase allows for backup in separate locations and increases entropy of seed, not sure how one can argue against that. Musig is something different and of course is most secure, with the tradeoff of complexity. The Bitbox article going around makes a comment against passphrases that someone might see you enter it in public....no! Passphrases are for cold storage only, never take a HWW out in public. If one needs to spend somewhere use Lightning or hot wallet with small amount on phone.