I think most of the African longer swords from the Congo were more status symbols than actual weapons. Some of their shapes are not really that practical in combat. Spears,clubs and bow and arrow were probably their best weapons and the dagger for real up close encounters. There are a few exceptions though such as in this sword. Heavy blade with a very well made point. Many tribes often used axes in war such as the two pictured below. The point here is that these weapons were developed based on the type of warfare that was common at that time and since the other tribes were not developing any new forging or heat treatment techniques that were producing substantionally superior weapons than there was no need for an arms race to make better weapons as was apparent in the Asia,Europe and the Mideast. Btw the viking sword was a complex wonderful piece of steel but was very expensive to produce and was quite costly to the owner to afford. The viking weapon of choice was the spear and the lowly axe which had a simple Iron head axes were easy and cheap to make. Battle field weapons evolve due to adjustments to the enemies tactics and weapons. In Japan the use of the straight double edged sword was abandoned sometime after 1276 after they realized that it was not very effective against the invading Mongols and created the tachi/katana or curved sword which was more effective. The style of the Japanese sword has changed very little from 1300-1800s because it did the job it was designed to do and it did it well. The same goes for African weapons the smiths just did not need to improve their techniques what they had did the job. Necessity is the mother of invention
Lew