I believe the JATR report recommended that the 'bare airframe' (i.e.with no MCAS) should be air tested for longitudanal stability. This suggests to me that they are not wholly convinced by the reasons given by Boeing as to why MCAS was needed in the first place. Could it be that not only does the stick force become lighter at a high AoA but, even if the stick back force is reduced/released, aerodynamic forces on the forward positioned engine nacelles at high AoA continue to pitch the nose of the aircraft up into a stall?