A collective of employees is not going to make better decisions than management. And if there are some who would, then they should be moved into management.
I only see the impact a union could have on improving morale and staff retention and therefore productivity if management/owners didn’t value it enough. These are things management are measuring and factoring in to their decisions. If management/owners are this bad then there isn’t much hope for the company.
And without a union management could simply provide autonomy to have the same effect. If Union force needs to be used to get mgmt to do the right thing for maximizing profits, it’s not really worth it.