My sentences:
(1a) Bob read more books than Fred. — We compare two nouns: "Bob" and "Fred".
(1b) Bob read more books than Fred did. — We compare two phrases: "Bob read" and "Fred did".
Sentences from here:
(2a) This fact makes the Korean language much simpler than English. — We compare two noun phrases: "the Korean language" and "English".
(2b) This fact makes the Korean language much simpler than English is. — We compare two phrases: X and "English is".
I can't find the parallelism in (2b) and, therefore, I can't understand the method by which (2b) was made up. Could you tell me please what X is equal to?