A leopard cannot run as fast as a cheetah. Can anyone

Sorry for the wait here...

This example comes from our Manhattan SC guide, and it's a really interesting question. What you're getting at is the idea that we can only use "as" to compare clauses and that clauses by definition are more than just a noun; they have verbs. Your sentiment and underlying principle are exactly correct. "Like" compares nouns; "as" compares clauses.

The thing about this example is that the "can run" after "cheetah" is implied and thus it is OK to just say "A leopard cannot run as fast as a cheetah." You are still comparing clauses, and since the GMAT prefers concise answers (note that I said "prefers," not "requires.), this is an acceptable modification of the sentence "A leopard cannot run as fast as a cheetah can run."