It's not rocket science. Defenses choked up on the Chiefs withe Cassel and Quinn behind center because they couldn't throw the ball with any accuracy beyond 5 yards (and even then it was a question mark). If you don't have to defend downfield it makes it a lot easier to bottle up the rushing game and defend the short routes. It makes Charles' rushing numbers that much more impressive.
You bring Geno (or any competent QB) into this offense and you're going to see success the second you loosen up defenses and make them respect the throws that these numbers show Geno can make.
Just my $.02.