Simple, the quality. iPhones are overpriced, but the quality is superb, a Xiaomi can be superior in characteristics and really cheap, but the quality sucks. Same with screens, a biiiig LCD with a really high refresh rate and high resolution may be great, but if it's a cheap screen with washed out colors or bad contrast, is never gonna be better than the pure inky delicious blacks of an OLED screen, and the OLED screen in the steam deck is ABSOLUTELY SUPERB, aaaand HDR