A lot of the debate surrounding whether or not Moana fits has to do with what the overall direction of this "overhaul" is. What is the new overarching theme for EPCOT, specifically (the area formerly known as) Future World, and how does Moana fit into it? Disney didn't create some ridiculous riddle for us to follow - they've been fairly upfront that the new "theme" of EPCOT is humanity itself. It's a celebration of all forms of life, from the wonders of the natural world, to the people who inhabit it. It's no secret these plans have been watered (ha) down a LOT, but the message is clear when we consider those original plans, what's actually being built, and what's been there all along. We just feign ignorance because of Disney's "magic of possibility" corporate speak and many people (admittedly, including myself) use the addition of IP to justify the argument that the park no longer has a clear purpose.
Consider the new neighborhoods and what they supposedly represent, and compare that to how little the layout of the park itself has changed over the years. World Nature is a representation of the natural world, World Discovery is a tribute to our manmade achievements, and World Celebration is simply a melting pot of different cultures coming together to celebrate the former. The grouping of the original pavilions was intentional in that regard, and what we're seeing now is only giving a name to what has been there the whole time. The park continues to carry on that original legacy, only with more emphasis placed on humanity itself and less on what humanity is capable of. This is probably most evident in what we've seen of World Celebration, where the the theme of communication is still prevalent but has taken a less literal role, focusing more on the idea of coming together to celebrate each other than it is on the futuristic technologies that help us achieve that.
Within the context of this "new" vision, Journey of Water absolutely fits. Whether or not Moana the character does is up for debate, understandably so, but the "the attraction would be better without the IP" argument is, to me, proof that the IP itself is irrelevant. If this is a truly educational and entertaining experience, where the characters of the film take a backseat to the overarching theme, then I think it will feel right at home between the Land and the Seas (even if the placement is a bit awkward). It seems as though many people have less problems with the attraction conceptually and more on its visual identity for that reason, which is a fair criticism. Let me ask then, if this was an entirely enclosed experience built in the empty Innoventions buildings, same rockwork and all, would that somehow make it fit in better? If there's one thing that modern WDI excels at, it's landscaping, and I have no doubt that this has the potential to seamlessly blend in with the architecture of this newly green EPCOT. In fact, wishful thinking though it may be, I'd love to see a lush reimagining of World Nature as a whole. The unique visual identity of the park is evolving, and I think what we're seeing now is an EPCOT that takes a more immersive approach to edutainment. We're no longer just learning about topics like space travel, transportation, the water cycle, etc through observation only, but rather, experiencing them first hand. It's a take that very well could be hit or miss.