Pretty much any nerf is going to be bad. Hak fishing is already horrible gil per hour to begin with. The last big npc price nerf I specifically remember outside of blinkers was in half. Blinkers iirc are what 1/4 what they used to be so yeah gunna suck.
There are a couple of soa fish that npc for 3k but don't bite any better than Haks so who cares. Most the fish that actually sell decent are used to make ebisu or lu shangs which will dry up after this. And the food market fish isn't exactly huge or have much room for more people getting into it...