Once you get entropy high enough, it's no longer the weak link in the chain. So sure, a 50 character long letter/number/symbol line-noise can have more entropy

Once you get entropy high enough, it's no longer the weak link in the chain. So sure, a 50 character long letter/number/symbol line-noise can have more entropy than a 6 word random passphrase, but it doesn't matter and has some drawbacks. By the way, for security questions specifically, I'd recommend passphrases. Often there are protocols where you need to say the security question answer to a human and they need to verify it. You're not going to have a great time spelling out a bunch of nonsense letters, and there's also more chance someone would be able to talk customer service into "oh I don't know, I just typed random keys" or something. Your password manager can likely do passphrases for you as well so it's probably no harder.