Spears

1. have longer attack range than swords and axes, have the damage of a sword but longer cooldown, useful for cavalry attack.
2. instead of having a knockback attack, it will instead have a piercing attack when attack while sprinting, can damage mobs behind in a straight line. (perhaps new enchantment, thrusting, which can increase the damage of the piercing attack)

3. can be thrown

4. can have the enchantments of swords except for sweeping edge (which for spears would be replaced by thrusting) and knockback (it wouldn't have much knockback)

Swords can have a slashing attacks, Axe are better for critical attacks, Tridents can be thrown, so why not have Spears as a melee piercing attack and for horseback attacks?