...which means the plane is lighter than the production version, so the results for the line aircraft are probably even worse.
Maybe. Maybe not. Test assets are loaded with all sorts of extra wiring, strain gauges, test instrumentation, data recorders, and telemetry equipment. And we have no idea what ballast (if any) was in the weapon bays to mimic/model weapons, nor the fuel state of the test aircraft.
I believe we should be much more cautious about making assumptions and drawing conclusions based on those assumptions.