8 is enough. 12 is a little bit better, but it’s the least of the reasons why newer cameras are better. Basically, they increased it because the sensors got better, so why not. Also, because the market is obsessed with numbers. But in reality, if you could change the camera on an iPhone that had 8mp to 12, and change the current ones to 8 - the current ones would still be better.
Same with the screen. Sure, a 1080p screen is a little bit better than a 720p one on a phone, but at the end of the day, it’s not a big deal. There are much more important aspects of a screen: mainly contrast, but also color accuracy, wide color, True Tone, etc.