I agree that it's sort of weird. Feels like stretching the concept to the limit in the name of justifying its placement in Fantasy Springs. That they sort of try to wave it away within the story suggests the choice of ride system is a liability to be excused rather than an asset to be embraced.
I can't help but think that there was an interesting opportunity within the Frozen IP to offer TDL a port or attraction that offered an experience of the, *ahem*, frozen parts of the sea which aren't yet on display in the park. Riding across a frozen fjord on a sleigh would still have fit for TDS, been different from yet another boat ride, and could serve the Frozen narrative by moving more naturally through both outdoor and indoor locations without the need for rivers that seem to run through buildings that have no rivers in them (even if they're not literally, actually running through the buildings).