Your reasoning isn't outrageous, but I put more value in fights closer to prime. As a comparasion, the 38 year old Mayweather outboxing Pac, who still is one of the best fighters around, is an excellent accomplishment. But still nothing compared to beating Pac at his best. But Kessler vs Froch 1 WAS close, and I agree Froch won the rematch convincingly. The skill difference between Froch and Kessler isn't very big, and you never know how one more fight during their primes would have turned out. But when it happened, it was Kesslers win ...
Froch got more popular names after and thru the tournament and obviously better television coverage. BUT Kessler in his prime was the man, if I remember correctly he basically fought every person available in the top ten lists of that division. If those fights were all televised globally people would rank him higher. You can't ask anymore of someone. Also shows how good Calzaghe was beating him.