How to get back old Wi-Fi-button behavior in Control Center?
The Apple site you linked to indicates how to completely turn off Wi-Fi and Bluetooth:


  If you want to completely disable Wi-Fi and Bluetooth for all networks and devices, follow these steps:
  
  
  To turn off Wi-Fi, go to Settings &gt; Wi-Fi and turn off Wi-Fi.
  To turn off Bluetooth, go to Settings &gt; Bluetooth and turn off Bluetooth.
  
  
  For the best experience on your iOS device, try to keep Wi-Fi and Bluetooth turned on.