Did he really though? Remember, losses don't count. And his wins aren't THAT superior to the ones on Calzaghes (if they are at all on a best v best basis). He has a slight edge due to number of top fighters over a shorter time frame. Dirrell, Johnson, Abraham, Groves etc aren't all that amazing. The impressive part was it being consecutive fights.
For what it's worth, Kessler thought Calzaghe would have won, maybe. Fighters don't often come out and say it straight like that, which is evidential, as he added a maybe afterwards. It should be noted that Froch and Kessler became very good friends after their first fight, so I feel like he probably added the 'maybe' as a sign of respect. Obviously Kessler is no psychic medium, but I thought it would be worth sharing... Especially because it supports my views