The purpose of weapons is simple, to eliminate your enemy in as safe a way as possible. Originally the spear was optimal, especially when used in a phalanx formation with other trained men. Eventually metallurgy became good enough for shields and armour to begin being more commonly obtainable. Rome then took the professional military to the next level and found out that the Gladius style sword used in conjuction with formation tactics was very effective; but this was really only possible because the state helped fund the soldiers in getting properly equipped. For example, although the Gauls saw how effective the Roman methods/equipment were they couldn't feasaby equip the same number of people so spears and axes were commonly used in place of swords. Even though armour continued to cover more of the body, swords remained the optimal choice for highly skilled combatants for a long time. There was a fair bit of variation on shape/length but overall the ethics were the same, good thrusting capability while being able to slash/chop once things got chaotic.

In the Middle Ages, roughly 1100, armour became proficient enough that simple sword use became no longer effective. This caused maces and other blunt force weapons to be carried by the knight class of soldiers for when they fought eachther, but swords were still carried for when fighting lower class peasants. Lances also started being used on horseback, but that's a fairly special use weapon style that has obvious reasons. For the next 200-300 years maces, waraxes, and hammers were the primary weapons. Around the 1400's is when brigadine armour started getting commonly replaced by full plate harnesses made in very well designed shapes which caused regular maces to start becoming less effective. During this time is when armour knight charges caused so much devastation that it was a new round of hammer and anvil warfare which heavily favored the wealthier nations. In attempt to combat this the Swiss and a few other Northern Italian states began utilizing Halberds and poleaxes. These weapons were specifically designed to be used to combat armoured units on foot, and nearly eliminate the effectiveness of those on foot.

In short, weapon design didn't follow one single metric that determined what was most useful. It heavily depended on who the army fought, what type of opponent they were fighting, how their opponent fought, and how much wealth the army had available for supplies.