The new C63S PHEV has also been panned because of its weight, plus the 4-cyl engine. It's 4,750lbs vs. ~4,150lbs for the prior gen, which was V8 but RWD. So in going PHEV, adding AWD but losing 4 cylinders, it gained ~600lbs.
This M5 already had AWD, and basically the same engine. So in simply...