Yeah. ArchiCAD lacks a bit here. But you should think of the toolbox as tools, not as the name implies: walls, slabs, roofs and now shells are amazing tools that can be used in different ways.
Wall tool -> vertical elements that can be slanted and don't have to go only to the next floor. Slabs -> can also extend several floors and can be faster to adjust for massing. Etc.
For massing, I've used Zones, Slabs, Walls, and even the Basic Shapes objects included. They all work great.
Just because there is no "Conceptual massing environment" button doesn't mean you can't do massing in a simple way, without setting floor levels, making proper walls, slabs etc. You already have an integrated massing environment. Rethink the toolset.
Best regards.