No, it's still safer than writing down your seed words in plain text, there's no debating this, otherwise this puzzle would already be solved.

The obscurity is still there, because in the real world you wouldn't know what method someone used to encrypt their seed words. Here I gave out the exact algorithm used and hints and still nobody solved it. If I just posted an encrypted seed word mnemonic here without the method I used and without any hints whatsoever it would be impossible to crack, same is when a thief comes across your mnemonic.

I know about using an extra passphrase, as I wrote on github:

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The purpose of this is to be able to safely write down your mnemonic seed words, not having to worry about a thief stealing your private keys, and in case something happens to you, allow your family to regain access to your wallet without needing to know a complex passphrase (TREZOR/Ledger), as all they need to know is the dates you used and the method to decrypt the words (pretty easy if it's in-family birthdays). Gather them around the table and do a couple of examples by hand. If you have a TREZOR or Ledger hardware wallet, having a complex passphrase as the "25th" word is more secure, but the more complex the passphrase is, the easier it is for your family or even you to not remember it at all (unless you wrote it down, which is a security risk in itself). If something were to happen to you, having a simpler passphrase (such as names or birthdates) would make it easier for your family to remember and access your wallet, and you could use both a passphrase and encrypt the seed words with a date shift cipher for extra security.

You would however need additional hardware (TREZOR/Ledger). MetaMask for example does not support the 13th/25th passphrase, so if someone has a MetaMask seed how would you safely encrypt it? My method works and is secure.