Just so that it’s definitely clear in case anyone doesn’t know:
All works created are automatically protected by law, by default. That’s not a Wattpad rule, that’s a copyright law rule. You don’t have to “copyright” or claim anything or make any statements. Just by putting it somewhere people can see it, it’s definitely yours and protected by copyright law (though I’m not a lawyer and this does not account for what I’m sure are the super weird fringe cases that exist somewhere, so this is in no way legal advice).
Which means anything you do (copyright page, getting a logo, who knows) is entirely for peace of mind or your own habits, whatever they might be. The copyright section on Wattpad isn’t us offering copyright, it’s just you displaying to people which one you want your story to fall under, which is why if you don’t select anything it defaults to All Rights Reserved. You have to state otherwise for it not to be.
Anyways, I have also never seen any evidence copyright pages do anything to remove or reduce copyright infringement, though I have not extensively tested that theory in any substantial way. They can cause some reader friction as people just want to get in the story but the general reasons people copy content (don’t understand copyright, think credit alleviates, think minor changes to names alleviates, just want to share with people who can’t afford, think more people should know) pretty much ignore or misunderstand copyright anyways.
And, just to be super clear on the plagiarism front, plagiarism is legal, it’s just generally unethical or frowned upon and depends very much on how much people feel the idea is unoriginal. But ideas and concepts are in no way protected by copyright (if they were we would’ve run out of things to write about a long time ago), so if your worry is that someone might steal your idea or concept, well that’s just kind of the world of writing. Your story is probably eerily similar to a story you’ve never heard of, halfway around the world. The entire concept of ownership of ideas and even copyright is all a very modern concept in human culture, it’s not something we really cared about much before (if anything the opposite was promoted). I don’t know if people know that or not, I just see the word plagiarize and copyright used interchangeably when they are very different things.
Anyways that was mostly for clarity purposes, and most people here are talking about the peace of mind it brings them, which is totally a fine reason to do any things you do. Just want to make sure nobody has misunderstandings around copyright applications.