two people using the same seed will be able to create the same image.
In my experience ONE person using the same seed will not be able to create the same image. I can feed an identical prompt into an AI artist 100 times and be handed 100 similar, but different pictures at the end. This may change as AI science evolves however.
so nothing stops me from saying “Hey, generate an image of Kirby”.
Every AI image creator has blacklisted words/tags for preventing copyright abuse or prevent creation of offensive images. Most AIs won't draw you pictures of Disney characters (anymore). Many AIs won't draw pictures of Jesus or public figures like politicians. No AI on the market will draw you a gory execution. The managers of the AI in question just have to implement a blacklist about it and they can stop you from running prompts for whatever they want.
There's also nothing stopping you from sitting down at your desk and drawing a picture of Kirby with a pen. When you're done, do you own that image?
I agree with you that AI art shouldn't be copyrightable or at least, if it is, there should be some significant hoops to jump through. But I don't think the arguments given here are good reasons why.