Bad product design = conceptual debt. It's a nice way to be able to say the costs you incur from making bad design choices early on, that now need to be dealt with and can be fixed.

But the concepts are not only in the product design, but also reflected in the software system architecture, since that will reflect the design.

One weird thing that happens is that developers insist that there is some sort of technical constraint, and then the product design reflects the software system architecture, rather than the software system architecture reflecting a product design well suited to users' mental models.