This is no "defect", the screen is as it is. MiniLED has blooming, either this is an issue for a person or not. If you don't go looking for it, you'll barely notice it. Most people don't know what it is and won't even register it's there.
Even though I think OLED is way better for video watching/HDR, I would buy a new iPad with miniLED if I needed to upgrade, it's better than the previous version. Other than trying to milk profit, I also think they went for what is best for wide array of use cases. The miniLED version has an advantage in brightness, which is better in bright rooms (a.k.a using it for business, not consumption).