Currently in the latest version of 2.2.0, developers can only use arcpy.mp to change the map extent in the Map Frame but not in the Map itself.
Map Frame is an element of a layout, but for many projects there's no need for a layout, as you may want only want to view the result map on the screen and you don't really care about the layout of a printable document.
And there are many cases that you want to zoom the map to the selected features and put focus on an particular area. To do this, logically the user should be allowed to set the extent of the camera for the specified 2D map. But this function is missing or not working.
I can only hope this function will be implemented in the Map class ASAP.