Its a subjective article, at this point they are feeding a bunch of data into a computer and laying it out for debate. Its impossible for that data to be correct because season itself will include a lot of variables that the statistical model will not include.
With the wages/output model it encourages debate that for all his skill, his output data in this model makes him overpaid, and other player produces a fraction of his output, for a lower wage. The analysis is then he is under paid.
Whether the article is correct or not it stimulates debate. Then is that in itself worthwhile.