At points in the season you could see a GT500 NSX running at 1149kg, theoretically anyways. The Aston Martins were at 1183kg last time they raced.
I would not say Class 1 aero is more extreme than new GTE
Class 1 has more freedom to use certain devices (GTE is limited to two diveplanes mounted on the front per side while Class 1 can go nuts, and they get fender louvers), and can cut away bodywork along the sides where GTE can't, but for the most part it's much more restrictive in where and how much you can modify bodywork, and with the 2017 rules in particular the underbody is almost pathetic in comparison.
Plus GT500 cars are narrower and have to run a skid block.
Take the back of the rear fender, GTE cars all cut that away entirely up to the 350mm free area for the rear bumper while Class 1 can only have a 200x250mm rear facing duct that the tire can't be seen through. The front bumper modification area for Class 1 is only 275mm tall with heavily controlled ducting while for GTE it's 350mm and pretty free. The GTE car can in theory run a longer front splitter if the production car has a long enough overhang (the Ford at least presumably manages this), plus the contour of the Class 1 splitter is spec while GTE cars have very developed 3D shapes. GTE car has a 250mm tall, 1400mm wide more or less free diffuser up to 1150mm (maybe on the Porsche) while the GT500 is another (presumably still) spec contoured part 105mm tall, 1160mm wide, and 1050mm long. (it used to be 205mm tall)
When you put it against a Ford GT it completely loses any advantage having a "prototype" chassis might have given it in internal layout or car setup too.