Having a say in the contract you end up signing (which may be at a variety of different companies) is more personally useful to the individual than having a say

Having a say in the contract you end up signing (which may be at a variety of different companies) is more personally useful to the individual than having a say in the specific contract of a specific company. So the claim that unions give you more say in the employment conditions of a specific company is irrelevant because it's an optimization towards the wrong objective.