Ok since this is not really answered... Hypothetically, If I'm a maintainer of this project. I decided I hate the implementation, it's naive, horrible performance, weird edge cases. I'm wiser today than 3 years ago.

I rewrite it, my head full of my own, original, new ideas. The results turn out great. There's a few if and while loops that look the same, and some public interfaces stayed the same. But all the guts are brand new, shiny, my own.

Do I have no rights to this code?

You have all rights to the code that you wrote that is not "colored" by previous code. Aka "an original work"

But code that is any kind of derivative of code before it contains a complex mix of other peoples rights. It can be relicensed, but only if all authors large and small agree to the terms.

You have rights, but if it's a derivative, the original author might have rights too. If you made a substantial creative input, the original author can't copy your project without your permission, but neither can you copy theirs.