Gains from productivity will accrue to those with the most bargaining power. Whether that’s the employee or the employer is going to depend on the exact circumstances (realistically it will be some mix). Hence why factory workers today get paid more than in the 1800s (and factory owners as well!)
> Gains from productivity will accrue to those with the most bargaining power.
That's true. And employers have been consistently the one with more bargaining power, and that's why our wages haven't kept up with the productivity gains. This is also known as productivity-pay-gap.
We, the working class, are supposed to be paid roughly 50% more than we are paid now, if the gains from productivity were properly distributed. But they are not, concentrated to a large extent in the owning class, which is what's unfair and why we, the workers, should unite to get what's rightfully ours.