ArcGIS Earth needs a high resolution base map option. The current options are not high resolution enough for line of sight planning. Google Earth has a much higher resolution base map.
The line-of-sight tool/elevation profile tool should have an option where you can choose (additional) height for each individual point.
The zoom should have a settings option so that it is dependent in real time (even while zooming) to the height so that it is not so sensitive that it puts you into the ground very quickly. I am sure there is a better way of phrasing this.
When you select a point/line/object on the map, it should highlight that saved item in the table of contents so that it is easily found. Points should also be easier to move. When adding a path, there should be an easier way to finish the path (double clicking often times does not work). And path lines should also be clear crisp lines even when draped, not just while relative.
