In the original comic it is shown that entropy of these passwords is still higher than the method with random words and substitutions. That means more combinations even with full knowledge of used dictionary

The whole point of the xkcd comic is that even if someone is using the same dictionary, the phrase has sufficient entropy to be secure.

They're not bad, if the password is long enough. So if you have 3 shorter words, add another word or two to increase it's length.