Thanks for the recommended reads, enjoyed them and they're hitting on really similar notions. Well cited comment :)

Conceptual debt is product design debt like you're suggesting. In particular, I think of it as a subset of product design debt that has to do with domain modeling as you suggest vs. having the write domain models but having poor user flows around those core concepts.

Unlike user flows, concepts are also reflected in the API & Object Models in your codebase so those may be trickier to change than the user flows that revolve around them.