That brightness, at that price, is a joke. Not just for Scar 15 but all ASUS ROG models that are stuck at 250-300 Nits.

My gaming setup is in an open-window room, and it's incredibly sunny all year where I live. I'd like to see details, shadows, and outlines in games and movies, when the scenes are taking place in a dark background.

To give some real world context, HP Pavilion Aero 13 is a budget laptop with a "520 Nit QHD IPS" display. Now that, is a $600 laptop that has been selling out like hotcakes since its release.

So why can't OEMs manage to put the same display with higher response times on a $1000+ gaming laptop?? Cost is certainly not the issue here.

What I have noticed is that IPS higher response times are achieved by lowering display contrast.
And this makes sense since liquid crystals will make smaller angle of rotation to achieve the desirable light refraction to obtain the specific colour.
The IPS response times are limited by liquid crystals viscosity. Hence there is the technology limit that will never allow to achieve 1000Hz refresh rate. What I see from your numerous tests, the max true (not the advertised) refresh value for IPS panels nears 100Hz.
But the good thing is that AMOLED and OLED panels are capable to yield 1000Hz refresh rate with their 1ms response time. And at this high refresh rate, the motion blur can be minimised to the level to get CRT-alike picture clarity in motion scenes, according to Blur Busters.