a1bill,
A simulation is an approximation of what is thought might happen. As far as many people know the performance envelopes of the F35, be these software, aerodynamics or communication performance envelopes have yet to be established.
As such it is quite easy to give the F35 performance characteristics in the simulator that show the plane up in a positive light, sadly these performance characteristics may well not be the ones that the final IOC / FOC aircraft has.
You may recall that according to the simulator the F35C could land on an aircraft carrier, when the test aircraft tried to land on a dummy deck with arrestor wires it became apparent that a redesign was required.
A very good simulator as CM states is good at showing the effects of changes to a system not necessarily the interactions of two systems.
I think that we all accept that the performance of the F35 is as yet an unknown quantity thus difficult to accurately simulate, how much comfort do we have that the performance characteristics of the red force is accurate?