I see your concerns. You are right that Pareto optimality is not about justice. It is about fairness, and it is true that what is fair is not necessarily what best approximates justice. Awarding a woman financial compensation for rape may be fair, some spiritual sphere miracle excepted, however, justice — restoration of her virginity (her sense of never having been violated) — is impossible.
Note, however, that applied correctly, Pareto optimality is not about maximization or minimization. It is about optimization. The fairness principle embedded so approximates justice, however, that it should be sufficient in context of capitalist economies.
The kicker? If workers’ pay are optimized, as opposed to minimized, they are more motivated and improvements in motivation can increase revenues to the point investors reap returns that are as high as those associated with minimization of wages that induces lesser revenues.
Given you are focused on the fact that it is workers who have the capacity for producing the goods and services, however, an argument with which I have some exceptions, you may not find Pareto optimality a strong enough concept for your concerns. But then it seems you tend towards the Nordic countries’ interpretation of socialist capitalism, which has been shown to work.