Ipad pros: enough brightness (nits) to make your eyes bleed who does that high of ratio? In direct sun maybe.
That's not the point of high nits. We're not talking about an all white web pages on a screen cranked up to maximum brightness. In fact, if for example you're doing just text entry all day in an office, you might want to set up your screen at 120 nits or something like that.
Instead, for high dynamic range content, we can have a very dark scene but with very bright highlights, but with detail still present in those highlights. Or we may have a blue sky with clouds with detail in the clouds, that you would not otherwise be able to resolve if the screen maxed out at say 500 nits.
With a screen that can't go as bright you have two main options when dealing with very bright highlights:
1. After a certain point - the screen's max brightness - all whites are the same. Bright and brighter are all displayed the same as a sea of white, because everything above the max of the screen is clipped.
2. Whites can be re-mapped on a gradient to be not as bright, so bright is a little darker and brighter is near the max that the screen can display, but the problem here is a lot of whites show up more as bright greys.
This is not a high nits image, but I'm using it as an example to illustrate a point:
You could design a scene where a highlight is say 1000 nits, but with parts 500 nits and parts 750 nits and parts 1000 nits. However, the overall scene is quite dark because most of the image is dark. A 1000 nit OLED screen would be able to show the true blacks as actual true blacks, but would also be able to differentiate the details at 500 vs. 750 vs. 1000 nits in bright highlights. OTOH, a 500 nit screen that clips whites would show all those highlights at the same 500 nits with no differences between them. Or if you didn't want to clip whites on that 500 nits screen, you could remap the whites to show more detail, up to that 500 nits maximum.
Here you can see that with the screen that maxes out at 400 nits, not only does the remapped white look grey, it also shows less shirt detail than the 650 nits screen.
Sony used to master its movies to 1000 nits. Such content would look best on a 1000 nit screen, even if the average brightness is only say 100-200 nits. However, I believe going forward Sony will be mastering their movies to 4000 nits. And some video games are already mastered to 10000 nits.