pikes are not invincible -- Spanish dealt with Swiss pikes by using short swords and bucklers to lift the pikes.
phalanx also has a weakness in that you cannot ever break formation -- hence it's vulnerable to skirmisher tactic -- long range hit and run. And it is vulnerable to flank attach as it cannot change direction quickly. Roman dealt with phalanx with flexible formation to move out of the way of the phalanx.
Qin army was also better equiped, on average, than the Greeks -- the weapons and equipments are mass manufactured from standard design. The standard of manufacture are good enough that parts are interchangeable. The reason Qin stayed with bronze weapon is not because iron was not available, but because bronze weapon can be mass produced by casting, while iron requires forging.
phalanx also has a weakness in that you cannot ever break formation -- hence it's vulnerable to skirmisher tactic -- long range hit and run. And it is vulnerable to flank attach as it cannot change direction quickly. Roman dealt with phalanx with flexible formation to move out of the way of the phalanx.
Qin army was also better equiped, on average, than the Greeks -- the weapons and equipments are mass manufactured from standard design. The standard of manufacture are good enough that parts are interchangeable. The reason Qin stayed with bronze weapon is not because iron was not available, but because bronze weapon can be mass produced by casting, while iron requires forging.