This arc literally only exists so that Robin has enough time to become "one of the crew" so that Water 7 and Enies Lobby don't become the "Aw man we totally have to risk our lives and declare war on the world government for that lady we just met." arc.
Try to prove me wrong, the only significant thing introduced was early haki. That being said it was really fun and is one of my favorite arcs.
Her introduction to the crew was so poorly handled. She should've at least taken a stronger stand and had a bigger change of heart against Crocodile so the straw hats at least know she's good before they take her on
>a bigger change of heart against crocodile
she was never not against crocodile in the first place. at most she was indifferent. the fact that she has drifted from one organization to the next everytime the previous one falls is a huge part of her backstory. Crocodile was just another phase and so were the strawhats at first.
This. The idea of sky islands is a big deal. You can't just have them pop up without having established them. And they have. Nami went to one during the timeskip and Kaido jumped off one. If that arc hadn't established them, people would be wondering what was happening.
Also, it set up Enel going to the moon, which I still think will turn out to be important later and might be the ancient weapon Uranus. Or even Raftel itself.