I like that Dell display (I mostly use Dell and LG displays) and most people should certainly save the money. The areas where the specs aren't the same are really significant though (e.g., resolution, as you noted, is a major difference despite only being one of the specs. Brightness, dynamic brightness, and size are also quite significant and drivers of major cost differences in just about any monitor comparison.)
If you're only using it for light HDR work, both are almost equally usable, and if you're mastering HDR content all the time, you'll need a dual-LCD panel anyway (as the sony hxr-310).
But you're right, the additional 3000$ are definitely noticeable - but if they're noticeable enough to justify that price tag is another question.
Agreed; ultimately the XDR is for people who, for whatever reason, just want a really nice, large monitor in sync with macOS' color management enough to pay the premium.
Here's a spec overview for those unfamiliar. https://www.displayspecifications.com/en/comparison/4f37c07a...