The highest grosing fight was at the Heavyweight division

The highest grossing non-HW fight was at the welterweight division

This sais alot about both divisions. However I do agree that the welterweight has bin a huge division throughout hisory. And it has rarely cooled down especially since the late 70s with the great legends of Benitez, Duran, Leaonard, Hearns. Then to the 90s with Whitaker, DLH, Trinidad. Now it's Mously, PBF(I expect he will move back down after the DLH fight), Cotto, Williams and Margarito among others. This is certenly a great time for welterweights, it is by far the hottest division right now.