Why is it unfair? This is the time when we needed him and he couldn't produce. Whether a guy can stay healthy and produce through injury is a big consideration if you are talking about giving him big money or making him the centerpiece of your team.
You're making my point. Even when Johnson was dominant, he couldn't carry a team because halfbacks just don't do that anymore. Now that he's just another guy, a fate that befalls halfbacks faster and more frequently than other positions, his contract is a massive albatross.