Must have GCD avaliable to move waypoint marker.

[Velox]

The waypoint is not an actual ability so I fail to see why it was implemented this way.

Actually, this is probably the exact reason why it was. Remember the actual code that handles AoE skills already exists in the game engine. This allows the devs to just create the waypoint marker from this class without having to create it as its own object. What this means is that the marker is a ground-targeted AoE skill that does not do damage nor buff/debuff anything. This way the devs wouldn't have to reinvent the wheel since all the code is already there and can easily be tweaked in a fraction of the time it would take to design it from scratch.