Many people think having the most advanced AF system in modern DSLRs is enough to ensure sharp shots. It still takes a lot of user experience and dexterity. Ask sports photographers, or those who shoot dancers in low light at ISO 12800 at 1/400!
so true...I shot a HS football game last week where i HAD
to go to ISO 12,800 and above(even at 2.8 and 1/500th)....the 1DX AF was still spot on and i had no trouble at all acquiring focus. (quick to AF and not one instance of hunting)
example...ISO 16,000 at 2.8 and 1/500th. and this shot is very heavily cropped to boot.