It's not cumbersome really. The tutorial shows how to add accurate waypoints, hence the zoom in while standing at the desired location steps.
However, there is nothing to stop you adding rough and ready waypoints without visiting the location. It helps to right-click the Carbonite map and stop it following you while you set up the various waypoints. Then just move the mouse to desired location, using the coordinates display as a guide, adding each waypoint once the mouse is in roughly the right spot. Once you get going this is a rapid process.
By way of example, when I added the midsummer event npc and fire locations to my Favorites, I started by using rough and ready coordinates gleaned from various forum posts. As my main character visited each location I refined the waypoint positions. This meant that on subsequent alt runs I didn't have to spend any time compensating for inaccuracies in the forums coordinates / location descriptions.
That said, I do agree that it would be handy if you could directly add / edit coordinates directly into the Favorites window - but definitely in addition to the current point and click method.
