Please keep in mind that backlight uniformity and panel bit depth are not related. Bit depth determines the color quality, especially when dealing with alpha blending. True 10 bit is CRT color quality, but NO gaming panels in existence use true 10 bit color. Backlight uniformity is simply QA stuff. These panels are edge WLED backlit. I do understand you're frustrated with dealing with lotteries, and the only surefire way to avoid one is:
1) buy the panel locally and visit the shop and look at it before leaving the shop (which requires you to be lucky enough to live by a reseller).
2) Ask a competent engineer to open the panel and test a GREY uniform surface (Eizo monitor test works great for this) for backlight uniformity, over the phone, before ordering. You may have to pay a fee for this, and very few places will do this. However, they might be willing to test it for you, just to avoid having to deal with a RMA, but that's purely up to your haggling skills and how much they like you over the phone.
I would bet $100 cold cash that the PG248Q and MG248Q use the exact same true 8 bit panel. Notice pcmonitors.info does not have a review of the MG248Q.
Now I don't know if that panel was cherry picked, but they sure won the backlight lottery.