No, that chart meshes up pretty well with my AH experience, at least in AH1. I don't have enough experience in AH2 to say, but on average I'd say the Hizooka hits about 4x as hard as a .50, the MG-151 about 2.5-3X, and the MG-FF about 1.5 or so.
The La-7s guns and the Nikis gun rate above the MG-151 but below the Hizooka, don't know enough about the HO-5 to say but my impression was it hits about as hard as a Mg-151.