The conventional approach is to consider the ethical issue of fairness of allocation – the 'to each according to his need' side of the matter – rather than the implementation issue of earnedness of contribution – the 'from each according to his capability' side of the matter. The implementation issue addresses the systematic values.
The move from fair to deserved is the move from output to input, and it is the move from what's good for individuals to what's good for society. It represents an entirely different way of looking at a host of moral philosophical questions.
By moving from fairness to deservedness we can reframe a whole universe of moral philosophy. It's what the Bible is talking about – not the ethics but the effectiveness of a righteous social system.