Technically true perhaps, but from my experience the word selection is always way narrower than that, like usually from maybe the 2000-5000 most common words.
It's big enough to matter. 2000^5 ~= 60^9 so it's as strong as a 9 random character password which is usually regarded as strong enough, and far better than a typical 1 word with 3 or 4 special characters mixed in.
Still a big number, but not astronomically big.