I think the benefits of the tandem OLED over traditional OLED are brightness and longevity. If tandem OLED are going to add substantial costs to use, then it becomes much less attractive because a) 500 nit OLED laptops are plenty bright for most people, and b) there are a plethora of beautiful 3K OLED laptops on the market that are half the price of a similarly configured MBP. If I can invest half as much now and keep it half as long then upgrade to the latest-greatest in a few years instead of keeping my uber-expensive MBP for 6 years, I think I might stick with the former.
I presume Dell skimped on the OLED to keep costs down (they seem to be in money-hoarding mode lately with everything priced like Apple). But who needs 1000+ nits unless you watch a lot of HDR movies (on a laptop? what's the point?) or do HDR video editing. Otherwise, it's just too bright.