Strictly comparing by price, I would think this is much better/feature-rich to justify the large difference. This is definitely pertier tho.

Other than the visual differences in the output diagram, I think the other main difference is the way the table & columns are created.

dbdiagram is freeform text-based and parses that to generate the diagram, while in DrawSQL there's an editor supported by keyboard-shortcuts to do the creation.

Overall they achieve similar outcomes. Personally I think it's a well-built tool too!