The AMD Wriath Prism cooler is a really nice stock cooler, but it has one significant drawback.
You can see from the picture the outline left by the Ryzen CPU. You can also see all the uneven grooves in the cooler surface where the heat pipe itself is left to be the interface to the CPU. This unevenness allows for variation in the gap that heat sink compound has to fill. This leads to an uneven heat distribution and lowers the efficiency of the cooler.
Notice the smooth high polish surface of the Noctua NH-D15. This finish allows for a small amount of heat sink compound and a higher degree of surface mating area with the CPU. This leads to a higher thermal efficiency. Most, if not all, aftermarket coolers will have this high degree of finish.
In testing, the Wraith Prism cooler did indeed hold the CPU to 85C at full load when running Prime95. In general computing/gaming the stock Wraith Prism cooler is a good cooler. With a touch more work, it could have been even better.