I can see a few Skypiea parallels but nothing major.
The fake SG will turn out to be a teen or a weakling royal who does this kidnapping business in the basement of his lodge/castle.
As to why Shanks allows this - Shanks isn't
omnipotent lmao nor can we just assume the captured people to necessarily be good and without blame.
Next chapter they'll knock the giant down with a combo move (spiralling into agenda as to why it took 5 of them to do it). The mask will fall off and we will get either a giant nami clone or some mid design - either way the coolest it'll get is the current look (cries for old Roger)
The giant will be suspicious of Luffy at first and won't accept him as Nika probably but will reluctantly lead them out to explore Elbaf. Amazing Elbaf double spread either next chapter or the one after