Join Date: Mar 2012
Shaka's successful imperialism wasn't the result of weapons - weapons rarely make the difference in war when neighbours fight each other. The credit should go to discipline and organisation (both on and off the battlefield). Same for the Romans - they didn't win wars due to using sword and shield, but due to discipline and organisation (and numbers and industrial capacity (e.g., building fleets on demand)).
Thrusting spears were around in Africa long before Shaka. Shields were around long before Shaka.
IMO, "engineeringly incompetent" isn't an accurate description of swords with effective cutting edges, often effective thrusting points, and weight, balance, and length that make them easily usable weapons. If they have an unusual stereotypical appearance, but will effectively cut (and sometimes thrust), they appear to be engineered well enough. Often, they have ergonomic grips, blade cross-sections that give good stiffness for low weight, very effective cutting cross-sections, and features such as forward curved tips (e.g., sickle swords as in the OP) and pointy bits (e.g., flared-tip Konda swords) that will give fearsomely effective penetration on a cut. They no more deserve being labelled non-functional due to their appearance than exotic-to-European-eyes weapons like the kukri, kora, kampilan, and kris.