A wallet passphrase that no one memorizes is usually 12 words or 24 or more. Everyone keeps a note of their passphrase be it online or offline.  Many times it is seen that the wallet gets hacked but it is due to the fault of a wallet user. When someone connects their wallet to a fake site, hackers take access to that wallet. But yes, long passphrase definitely increases the security of the wallet.  Because it is possible to memorize a passphrase of 12 words or 24 words, but it is very difficult to memorize more words, so it will be more secure.