I don't really see what there would be to argue about? There is no difference- Your weight+ bike weight+ clothing/gear = total weight. You already stated some of the reasons why a lighter bike is more efficient...And if you want to lose weight- RIDE the $%&* outta your bike and have a healthy diet, simply put. Only difference would be..The leaner and more fit YOU are the more you will be likely to ride and the better you will perform. Right?