Look...
Kishi threw a bone to all the Itachi fan boys. Kishi probably likes Itachi more as a character than he does Nagato.
Oh, and Susanoo is an extremely cheesy overpowered ability that degrades the manga in many ways by simply existing as an ability. There's nothing remotely "ninja" about it.
Do I personally think Nagato had a better, more compelling and original story over Itachi? Yes. Do I find Nagato's abilities like Shinra Tensei cooler than Itachi's? Yes.
But Kishi didn't and fans drool over the androgynous sexually confused, nail painting, long eye lashed Itachi.