Not necessarily. Fighter aircraft size/weight has increased as engine technology has improved. Did you know that F-35 is in the same ballpark as the F-15C in terms of empty weight? Another thing to consider is that even though sixth generation fighters are all doritoes planform wise, there are novel aerodynamic approaches such as movable wingtips and collapsible control surfaces that can allow them to perform stunning maneuvers should the (highly unlikely) need for dogfights arise.
