Since they're trying to construct a rocky mountain landscape, which of course doesn't exist in Florida, I think that a retaining wall for a rushing creek seems pretty darn necessary, and I cannot see how this could be seen as anything out of the ordinary, given the extraordinary circumstances. This may be narrower than RoA, but you can see that there appears to be a sloping grade, so this thing will probably be moving pretty fast, unlike RoA, which was pretty still. With that and the waterfall, it should make a pretty pleasant sound, as well! Doubly nice, is that it should mask the ride sound pretty darn well, too.
In my opinion, if a rocky mountain landscape doesn't belong in FL, then neither does a European Village, a castle, or desert mountains. Whether it fits in with everything as well as a Missouri River is up to both personal preference, and how well they pull it off from multiple vantage points.