Anisotropic filtering is not magic. It’s not a way of saying, “make this look good”. It’s a specific filtering technique designed to solve a specific filtering problem.
A problem that your particular rendering case does not have. You are scaling the image uniformly. Isotropicly. There is no anisotropy, so there is no anisotropic filtering.
Furthermore, an implementation is allowed to completely ignore your anisotropic filtering settings if you have no mipmaps. This is because aniso works best with mipmaps, and will not work nearly as well or efficiently without them.
So, you should get some mipmaps, use GL_LINEAR_MIPMAP_LINEAR min filtering, and then you’ll get a better result.
As Alfonse said, you scale your image isotropicly, so unless your window will be 6400x6400 or larger you need mipmaps to get the best rendering/filtering results.