Why are the Chargers such big favorites over the Chiefs?

The Chiefs have a better record, Better division record, They lead the AFC West, And have already beaten the Chargers once this season what is it they have thats so special? Their defense is "#1" when is reality its mediocre. Philip Rivers is good but he cant win by himself. He has no real receiver besides Gates and maybe Crayton. Jackson is out. Their running game is horrible. Who is Ryan Mathews anyway? Tolbert is good, But so is Kansas City's defense. The Chiefs have alot more weapons with McCluster, Moeaki, Bowe, Charles, Jones, and Tucker. On defense they got Tamba Hali the sack machine. Derrick Johnson(ILB), Brandon Carr(CB), Eric Berry(SS), Glenn Dorsey(DT) etc. Well i wanna know the playmakers that the Chargers have. Thanks.