That's because if EMFH were to stay the same as now, it would 100% share CD with the PvP talent trinket. Not only that, nobody actually expected EMFH to stay in Legion with the PvP talent trinket. EMFH in Legion also works like WotF where it shares a 30 sec CD with the PvP talent trinket. Compare that situation to WoD and you've got 2 ways to get out of stuns, arguably the strongest CC in the game and the easiest way to generate kill pressure.
I reckon humans will still take the reduced CC duration PvP talent because of how potent it is and because you'll still have a way to break free from stuns , somewhat similarly to US MoP undead mages who didn't take a PvP trinket due to blink but also because they had WotF during a period where Fear was the scariest form of CC.
In legion you'll also be able to change your PvP talents in the arena waiting room iirc. Which means that if a human faces a comp with scary stuns, it won't even matter whether EMFH breaks all CC or only stuns.
Even if you compare Legion EMFH to live EMFH. Having a stun trinket and a PvP trinket, I bet you human would be even stronger.