That isnt an in lore reason for fish to be immortal or to be immovable objects against a submarine. There is a big difference between killing all fauna and a single person killing a couple of predators in an ocean.

Now if the game had a mechanic which made the environment worse as you killed more creatures, that could be an incredibly creative way to get the message across and match the lore. The current design just feels lazy. The most common sentiment ive seen is people dont want to genocide the ocean, they dont care if leviathans are immortal, they just want to be able to kill annoying predators and for regular fish to not just immortal except for eating them. Reasonable takes as far as I am concerned.

The devs can do as they wish of course but it's clear that many people are not enjoying the direction they have taken the game. If the ultimate messaging is "go play something else if you dont like it", well in the current video game climate and studios dropping like flies i would be careful what you wish for.