I wonder if you string together enough words can it be a valid key?

I would hope so, sentences and words are some of the most secure passwords/phrases you can use

Words are the least secure way to generate a password of a given length because you are limiting your character set to 26, and character N gives you information about the character at position N+1

The most secure way to generate a password is to uniformly pick bytes from the entire character set using a suitable form of entropy

so you are saying 44 bits of entropy is not enough. the whole point of the comic is, that 4 words out of a list of 2000 is more secure then some shorter password with leetcode and a number and punctuation at the end