Is a qualified employee's repeated assignment to tasks, based on his manager's recommendation of his efficiency, considered Haram (forbidden) and an injustice to his less efficient and uninterested colleagues?

If the criterion for selecting individuals for tasks is solely competence, then repeatedly choosing based on competence is an obligation upon the manager, and this is not considered an injustice to less competent employees. This is the essence of justice, which means equal treatment for equals and differentiation between those who are different, not absolute equality. Sheikh Ibn 'Uthaymeen clarified that justice is giving every rightful person their due, and that the Holy Quran enjoins justice, not equality, which might necessitate equating things that wisdom dictates should be differentiated.