Difference between 10bit 4:2:2 and 10bit display panels
The bit depth and the sub-sampling method are related but different parameters of the imaging system. As you noted, the bit depth determines how many different colors the system can display. The more colors that can be imaged, the closer to reality the image looks. You also get fewer quantizing artifacts.

The sub-sampling method is a form of compression. Human vision is less sensitive to colors than it is to luminance, or black/gray/white, information. By only sampling some pixels for color, the system saves data by trading off some resolution.

(You should note that the "better film cameras" you reference in your question probably use 4:4:4 sub-sampling and better/professional video equipment use 4:2:2.)

You can have any combination of bit depth and sub-sampling. So a system can be, among other possible configurations:


8-bit 4:2:2
8-bit 4:4:4
10-bit 4:2:2
10-bit 4:4:4