They way how Fatigue is right now is good!
I had a short time in the Austrian Army (1,5years) and from my experience the "Fatigue System" is pretty solid.
Its not 100% Simulation because in that case you would idle alot more :p
Its a good Simulation feeling with a bit of an Arcade touch.
Also you are not designed to run with a full Backpack and an Rocket Launcher.
The non Rocket Launcher Backpack Fatigue feels awesome and is pretty accurate on a short term view.
Ah one short thing i have the feeling that even after a long run you should be more accurate if you are lying on the ground.
PS: My English is poor i know.