The best explanation for the relative significance of the trans-Saharan and Indian Ocean trade routes is:
The routes were equally significant—each in its own way—as they both contributed to significant cultural developments along the routes, and worth cannot be measured simply by the goods that were traded.
This option acknowledges the unique contributions of both trade routes to cultural exchange and development, recognizing that the significance of trade is not solely based on the material goods exchanged but also on the broader impacts on societies and civilizations involved.