And then you have some retarded shit for every site that you can't possibly remember unless you're Rain Man and have to use crutches like post-it notes under your keyboard and password managers. These passphrases usually also use more characters so the fact you're getting less entropy per character is outweighed by the fact you're probably using more characters in the first place.
The xkcd cartoon just isn't wrong. Even if the attacker knows you're using exactly this as a technique, it only slightly shortens their time to crack your passphrase, which is probably in the quadrillions of years anyway, especially if you just smush a bunch of dictionaries together into a giant file and generate randomly from that.
I have probably a hundred different accounts in my password manager. Do you think I should use unique passphrases for each of them? The real crutch is password re-use, lowering your overall security because— as you say— you aren't Rain Man and can't remember a hundred different passphrases.
The main advantage of password managers is automating the selection & use of
strong,
unique passwords. It's true that this creates a single point of failure if someone were to keylog and steal your password vault. That's why physical vault decryption keys like Yubikey are important.
I realize there are also fancy attacks based on reading memory directly to scoop a password manager's master key, once they key has been unlocked with a master password + token. I don't know how common these attacks are in practice. It's also true that offline password storage (a notebook, old tablet, whatever) is immune to such attacks. If your PC has been compromised, though, they'll still get you when you type individual passwords to log in or renew sessions. So that's why it's important to reformat and rotate passwords occasionally.
If they're unique and sufficiently long, I'll concede that English passphrases are still good enough. Just did some back of the napkin math; there are 40,000 English words in common use per Google, so a passphrase of 4 common words (with reuse) has 40,000^4 permutations. At a single-GPU hash rate of maybe 24,000 h/s per Hashcat numbers I Googled, that would take 3 million years to crack with a dictionary attack. Good enough for anyone who isn't targeted by government agencies.