From a metal working viewpoint, carbide is desirable because it has higher strength at red heat. You might seldom see this when milling, but when roughing on lathe jobs, the engaged portion of the tip of the carbide will glow a steady, bright red. It nonetheless, keeps right on cutting.
The coating on top of the carbide is there to improve the lubricity and hardness of the tool. A hard coating needs to be backed up with something that is also very hard. Carbide makes a good base material meeting this requirement.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)