It was indeed fairly interesting. I have no complaints. And explains surely and for good the high number of episodes still needed for this arc.

What comes to the wings it's natural to assume the people of Shandia and Skypiea have common ancestors. No other way to really explain it. According to Norland the Shandians have abandoned progress and only regress. Maybe they aren't used to living on the ground, and have not been able to maintain their ancestral developed civilization. The Skypieans we see in the modern times (Luffy and Enel's timeline) seem far more developed than the Shandians.