Actually, it is modeled.
The extent to which it is modeled is basically a judgment call with no one "right" answer though...I mean, who are we simulating at the controls? A bantamweight or a 200 lbs. power-lifter?
If the 109 (as an example, there are other planes that had a rep for tough controls at high IAS) had controls that become too stiff to pull blackout Gs at say, 300-320mph IAS (as is the case in some sims), instead of the ~400mph IAS it takes in AHII, it WOULD change the capabilities of the 109 vrs. other iron in maneuvering combat to a notable extent. Having the "pilot" be more G resistant would have a similar effect. As it is, the 109 hardly has any problems with controls during ACM, it's only a big deal if one is trying to do very high speed bnz with a 109. But like I say, there is probably no "right" answer to the problem.