Resolution isn't everything. It's a brighter better quality screen. I guarantee it will look better than the 6 pro side by side. The few less pixels will not be missed
Peak and average brightness are two different things. Either way, I have never had issues seeing what's going on the screen unless you shone a bright light directly on it or something.
Typically brightness isn't what I'd consider as a factor for a quality display, rather instead color accuracy. As long as you can see the display enough to distinguish colors in most environments, that's what matters.