The Disney element is a barrier, 100%.
But I don't think "the series is dying" is relevant, without even exploring how true or not that statement is.
Is the performance of The Rings of Power the only reason you could imagine a Middle Earth area being successful? Are the viewing figures of Ashoka the only indicator of whether Galaxy's Edge was a smart investment?
What are the current viewing figures for the latest media from the Frozen, The Twilight Zone, Harry Potter, Jurassic Park, How to Train Your Dragon, Batman, etc. universes? Have they been better in the past? If so, by your logic, any attractions based on these properties are a bad idea.
Wanting to go on a well themed, exciting adventure with a pop culture character that has existed in public consciousness for people's entire lives, doesn't diminish because of numbers on a spreadsheet saying viewership is currently down.