If you can't stay awake after five Gs there is something wrong with you....
That's easy for you to say. You obviously fly long-haul, most probably with 4 pilots and 4-5 hours in the bunk. What about the guys flying two-crew for 7-8 hours through the middle of the night with no in-flight rest? No amount of G-days beforehand will stop the head nods and micro-sleeps during the subsequent descent and approach. What's less safe - 45 mins of controlled rest for each pilot during an appropriate time in the cruise, or two pilots falling asleep on descent?