You've got a typo there, it's 4K at 27" with 163dpi vs 6K at 32" with 215dpi, so 1.5× vs 2× resolution. Which actually has an interesting effect when working with content, as the Pro Display XDR either has to show a letterbox around UHD content, or has to stretch it in a very blurry way with GPU upscaling which definitely isn't useful for content production workflows.

And the halo effect actually is an artifact from the backlighting which can be resolved with the backlight recalibration cycle, which the Pro Display XDR does automatically and invisibly during times with purely SDR content, while it has to be manually run and is very obtrusive on the Dell one, that much is true.