With the UCI weight limit seemingly stuck at 6.8kg, 'lightweight' has been largely defined at that point, and brands have been able to focus their attention on improving other areas of the bike, instead of simply chasing grams in a race to the bottom (although, naturally, that is still a thing).
Where aero bikes often have to make compromises on things like ride quality, fit and user-friendliness in pursuit of all-out speed, lightweight road bikes have tended to become the all-rounders of road cycling, with development focused more on these important, but often undervalued characteristics.
Such are the improvements in these areas that many WorldTour pros still choose to ride lightweight bikes over their sponsors' aero-bike offerings, despite the apparent penalty in aerodynamic efficiency.