The Harappans can be called great architects and engineers

That statement is true

Explanation:

A strong proof for this statement would be their irrigation system. At that time, the harrapans civilization was among the first society who manage to send water to agricultural fields that located far away from water source. (Advanced architectural and engineering skills are needed for this)

Because of this, they managed to eliminated hunger problems and continuously improve their economic strength due to the large amount of crops they're able to sell.