You are assuming Wednesday didn't starve her piranhas just enough to cause serious injury without death. That is her kind of thing.
I wasn't assuming anything -- I was answering
CaptainWacky's question exactly as asked, which was whether piranhas could realistically have
killed those swimmers. Serious injury is a separate question.
But even serious injury is unlikely in a realistic scenario, because piranhas are small and their bites aren't as dangerous as the exaggerations of fiction. It's one thing to throw them a cow carcass they can feed on at their leisure, but live humans could probably escape them fairly easily, or scare them off with their flailing. Real piranhas are timid fish that travel in schools to protect
themselves from predators, not to hunt in packs as in the movie myth. Their bites are more likely to be warnings to drive off attackers than attempts to kill.
https://explorersweb.com/killer-piranhas-myth-or-fact/
So realistically, stressed piranhas might bite people that they thought were attacking them, in a situation where they were forced together and the people were flailing in panic. But those bites would probably not be enough to cause
serious injury or risk of death. And they wouldn't
chase after a human swimming away from them. Even starving predators have a sense of self-preservation and won't risk getting themselves injured or killed if they can avoid it. And piranhas aren't predators at all, just omnivorous scavengers.
Gomez: "Nevermore, I love you!" Just because we don't see people exactly like them, doesn't mean this isn't "their people".
Yes, but the fact that the story doesn't show them is exactly the problem. The story
asserts that these are their people, but what it actually shows doesn't bear that out, and that's bad storytelling. It's an informed trait, like claiming that a character is a genius but having them behave unintelligently, or saying they're a great martial artist but having mediocre fight choreography (I'm looking at you,
Iron Fist). A story's job is to
show us things, not just claim they're the case and then show us something contradictory. It doesn't matter that the writers have Gomez
say he loves Nevermore; they need to
earn that by depicting Nevermore in a way that justifies that assertion. And they totally failed to do so.
Even aside from that, just the way the students themselves were depicted was inconsistent and poorly thought out. Why the hell are vampires and werewolves terrified by the sprinkler system spraying blood? Why don't we see any classes about mastering their monster abilities, or indeed any classes at all besides the one on carnivorous plants? Why are the Addamses the only ones in this school of monsters who take pleasure in the monstrous and creepy rather than recoiling from it? Especially when the Addamses
aren't monsters themselves, Lurch and Thing aside; the women in the family are witches, but Gomez is just a guy with kinky enthusiasms.
It's just bad worldbuilding. They didn't put enough thought or care into creating the context for Wednesday to inhabit.