We had the highest rated QB, WR with the most TDs, and RB with the most yards last season. That was created for exactly the reason you described. It still wasn't enough to get us more than 1 playoff win because the defense couldn't slow down a strong passing attack.
If there was no cap we would have just signed Murray, but in the a resource restricted environment where every dollar and pick spent on offense is less spent on defense we must make choices.
We are losing because of poor defense and have been for some time. We needed the money to spend on Hardy and the picks to fortify defense. With a stronger defense we won't have to have an 1800 yard RB to win.