Jack Dempsey isn't beating ANY modern lineal champion with the possible exception of Leon Spinks or the bloated overweight version of Buster Douglas who lost to Holyfield...
When do you consider the modern era to have started? For me elite fighters today look no better than they did in the 20s. Some exceptions before that still stand out as well. I bet you can't find a MW who boxes as beautifully as Mike Gibbons.