I'm being a bit technical. I don't know if you can really make the argument that it's not more secure but it doesn't make guessing the password any harder and you might as well do a 2 of 2 multisig. W...
Passphrase use is more than just about entropy benefit, same as multisig.
Geographic separation can also be had with a passphrase.
A passphrase can be generated with a good password manager instead of generating one yourself.
The same care requirefd to safeguard a seed (or seeds plus more in a multisig) is used to safeguard the passphrase, not more not less and the consequences to losing the passphrase is the same as for losing the seed, not more not less.
Backing up a passphrase wallet is dead easy and foolproof, two components only, seed words and passphrase.
Backing up a 2 of 2 multisig is more complex and consists of 4 components and for 2 of 3, 6 components.
The argument that if you backup even one character wrong with a passphrase is true, and just like any other self custody setup, it must be recover tested first before using.
Geographic separation can also be had with a passphrase.
A passphrase can be generated with a good password manager instead of generating one yourself.
The same care requirefd to safeguard a seed (or seeds plus more in a multisig) is used to safeguard the passphrase, not more not less and the consequences to losing the passphrase is the same as for losing the seed, not more not less.
Backing up a passphrase wallet is dead easy and foolproof, two components only, seed words and passphrase.
Backing up a 2 of 2 multisig is more complex and consists of 4 components and for 2 of 3, 6 components.
The argument that if you backup even one character wrong with a passphrase is true, and just like any other self custody setup, it must be recover tested first before using.