It’s much more than calabrition. Actually they are entirely different displays.
Apples custom designed oled with different display panel materials and an entirely different calibration compared to Samsung own panels. if you look at the pixels under a microscope, you can see the difference between the apple and Samsung panel, it’s quite clear.
Think about the soc as well?
it’s not the Tsmc a12. tsmc is a fabricator (just like Samsung) that manufactures to apple custom specification, just like Samsung with the display.
Samsung even had to build apple their own dedicated facility for oled panels fabrication.
You don’t do all of that just to buy an of the shelf component.
Another example would be the Foxconn iPhone

. Because Foxconn are just the assemblers.
As someone else mentioned the only reason apple sourced Samsung was because of scalability But with lg, boe, and Japan display rumored to be entering apples oled supply chain, Samsung scalability lost the one edge they had.
Tl:dr Apple oled is a completely different display to what Samsung uses on their phones.