Hi Nick! Dimension is currently not aiming to be a modeling application. There are already many advanced modeling and animation packages (as you mentioned above. Dimension is instead geared towards designers, advertisers, marketers, and others who need to use existing 3D content to create mockups, visualizations, advertisements, etc.
That said, Adobe is all about creative expression and actually being able to make things is important for that. We do hope to add in some level of creation at some point, but don't have a timeline or any commitment to that yet. It's early days, so we'll continue to evaluate how to explore that as we move forward.