That is true.
Duplicating the existing functions would not be the case as the original functions would be removed. E.G. music player in control centre instead of the iTunes mini player, move Wifi/Bluetooth settings from top menu. Brightness in Control Center instead of having to go to system prefs (good if you're using a non-apple keyboard which doesn't have brightness buttons), AirDrop constantly on instead of having to open a Finder > AirDrop window to receive, and AirPlay Settings moved from top bar.
Also, you'll notice how the "About this Mac" and "System Preferences" buttons are located at the top. This implies that the Apple button (top left) will be the button to open Control Center. Also note the shut down/log off/sleep/restart buttons down below.
This makes perfect sense.
You have Notification Center on the right. You swipe from the right to open it/click the top right button.
And Control Center on the left. Swipe from the left/click top left button
Finally, Airplane mode. Unnecessary? What about wifi-only iPads? Airplane mode turns off wifi and bluetooth. It turns off cellular too on such devices, but still has a purpose on those that aren't cellular-enabled