HP Omen 16Z: 16.1" QHD 240Hz IPS, Ryzen 7 7840HS, RTX 4070, 16GB DDR5, 512GB Gen4 SSD, Win11H @ $1286.99 + F/S

300-nits IPS Display

It is illegal for manufacturers to make a perfect AMD laptop. By law, they have to screw up at least one thing.

The Intel version also comes with same display. But is it just the brightness that defines the quality of a display?

Brightness is a huge factor for me as I use my laptops in brightly lit rooms. I had to return a 300nit laptop for that reason, was just not bright enough. Also, most 400-500nit panels are usually higher quality panels to begin with. I have yet to see a 400 or 500nit panel with say 45% NTSC, but there are plenty of 300nit panels with that (I know this one is 100% sRGB, so it's okay in that respect).

The absolute minimum I now consider is 350nits, but prefer 400nits or above in laptops. Even Apple moved from 400 to 500nits in their cheapest laptops (MacBook Air 13).

The statement you are giving is too much generalized and not even true in lot of cases. It would be better if we consider the panel quality of a specific laptop rather than saying 300 nits panels are bad. In fact the opposite is true for a lot of laptops and let me give you an example.
Legion 5 Pro and 7 Pro has been offering these 1600P 500-nits panels since 2021 whereas the QHD panel (16:9) offered on Acer Predator series, Dell Alienware M15 and X15 series, Zephyrus G15, ROG Strix /Scar 15 series, were all 300 to 350 nits at maximum. That did not make the Legion 5 pro's display better by any means. Yes, it is bright and if you need that, then that is a better choice. But anyone, using their laptops for any kind of editing work professionally, then the Legion 5 pro and 7 Pro's displays are literally useless because they cover very low Adobe RGB and DCI-P3 color gamut, just below 70%. On the other hand, those so called 300-nits display I have mentioned, all cover near 90% Adobe RGB and 99% DCI-P3, making them far better choice in terms of panel quality. Anybody, planning to use those cosdtly laptops for professional work withouit external monitor, will always prefer thoose high color gamut displays.
The brightness may be a factor for some, for example you, but that is not the only factor while buying one. It simply depends upon what the user is planning to do. In most cases, somebody plan to do any professional work, will prefer a lower brightness but high color gamut display over a higher brightness low gamut display.

I am actually using Lenovo Legion 5 Pro with 6800H/RTX 3070 Ti version (in fact typing from it) and I use a Alienware m15 with 12700HX and RTX 3080 16GB with 240Hz 1440p 100% DCI-P3 one. The difference when you are doing editing work is hell and heven.

Do Slickdealers just use their laptops outdoors more than most people or what? The last few laptops I've owned have all been 300 nits or less and I usually find them uncomfortably bright at max brightness, at least for indoor use.