We already know that the panel in the iPhone X is lower resolution, lower ppi and significantly lower brightness level than the panel found in the note 8. So regardless of how much Apple were willing to pay samsung did not give them their best panel.
the resolution was chosen by apple, it is not just some random number. they always multiply the resolution to make scaling cleaner. with the 4.7'' phone it was x2 and with the X it's x3. and they don't go over the top, because it will have a bad effect on battery life.
the brightness is exactly the same as the LCD panel iphones. which means it was chosen by apple too.
so far it looks like everything was built exactly to apples specifications.
and we don't know which value apple uses for the brightness in the specsheet. OLED is very hard to measure, because the brightness is different depending on the content. which is why the full brigthness is a range and not a fix number.
for example: galaxy note 8 on auto brigthness: 560 – 1,240 cd/m2
560: full screen is white
1,240: 1% of the screen is white
and let's not forget: even if it was the exact same panel, apple can still choose to restrict the max brightness if they think it would hurt battery or the lifespan of the panel too much.
so what we do know is, it was made according to apples specifications. but we have no idea if samsung would restrict access to some tech. but i suspect that enough money would convince them and they are likely making a ton of money with the X and it won't hurt them a bit.
for everything else, we will have to wait for the reviews.