I dont think zeus had its range nerfed.
Some of its power was when Hera started eating him, so majority of big moms soul power went to hera, so namis black balls can boost him in a way.
If anything zeus just got a more inferior master.
However it is true, Nami isn't the real threat in the fight, Zeus is. She's still fodder that goes down in one tap and Zeus you can't really touch so Zeus gets the win and Nami gets participation points.
If anything she's a high tier fodder control type of character.