You raise a great point, but to me, Tiana’s next to Big Thunder is already quite jarring.many of the things that “just work” at Disney - shouldn’t on paper. The Matterhorn, submarines, monorail, etc. being a prime example. That area of the park is just perfect, but a complete thematic mess at the same time.
Splash may not have been a perfect fit thematically, but visually it was much more on theme for Frontierland than Tiana’s is.
Perhaps the issue wouldn’t be so pronounced if the Tiana’s and Thunder traded places. I think the problem is the “western town” of Frontierland (Diamond Horseshoe/Country Bears/Pecos Bill) is completely separated from Big Thunder by a New Orleans area.
I just get the vibe that Frontierland will be even worse than Adventureland (in terms of a hodgepodge of settings that don’t flow well into each other).