Unnecessary? Did you not see the tragedy and character development as well as the driving major crisis and events that spurred the ideals of each person in the anime as well as push the relationship between Nia and Simon to a depth of devotion that transcended the meaning of "love". Season 1, story wise had the maturity of a kid while season 2 aged with Simon in the underlying themes, while holding on to the ideals presented in season 1 that laid the foundation of season 2, and was a lesson about straying from the path, and the stubborn narrowed mindedness of adults' paradigms.
I'll agree that in Season 2 the world itself was interesting, political intrigue interesting, Character development Interesting, New character designs interesting,
Matrix style ending "I am the architect" not interesting. You have to agree the second season could've been much improved if they found a way to focus specifically on the power struggles in Kamina City and with the rest of humanity instead of pulling out that. Yes i'm aware Season 1 suggested the Spiral King wasn't the "Final Boss" but still.