Yeah, the funny thing is, if this guy had been sitting on someone else's roster, and Beane traded a 5th or 6th round pick for him, many people would be praising him for trading for a young player with high potential. But because he planned ahead and added him back in September, there are some amongst our fan base, that will criticize him for lack of effort.
No guarantee that Mathis pans out, but Beane should be praised for loading the bench early, rather than "panicking" on the last day of the trade deadline and expending a potentially valuable future draft pick.