If you'd read the review, you'd know that there is nothing "dull" about this monitor. Movie theaters run at around just 50 nits, so 250 is more than enough in a dark room. And True Black HDR 400 will temporarily blind you during bright flashes like explosions.
Not a single review- and I believe I've read them all - has complained about the brightness of this monitor. I currently own the AW3418DW and it's only rated at 300 nits. I've never turned the brightness or contrast above 60% in any situation, and it's plenty bright. For gaming in the dark , I drop those numbers to 40% contrast and 25% brightness.
You should base your thoughts on first hand experience, not a spec sheet. I've ordered this monitor and can't wait for it to arrive. It will be single biggest upgrade to my rig that I've ever made! 😉