Yes, it is. If you look closely, you’ll see something like a base layer/plate. It’s 10mm thick. The dovetail adds more stiffness against front-back movement, so no worries here.
Compared to a center column design, front-to-back and left-to right (or any mix of it) bending is inhibited by form and strength of materials. Laminated wood is also more rigid than, say, an extruded Aluminium column of comparable dimensions. Others use a similarly rigid construction as far as vertical setups go. Horizontal setups are easier to build for stability…but I like to have the films sit flat on a level surface.