There is no correlation between WAR and post season success. In other words a team with a higher WAR collectively is no more successful than a team with a lower WAR. Baseball is a TEAM sport. WAR is an INDIVIDUAL statistic with dubious value.
The Cubs drafting Mathis speaks more to the quality of the draft than anything else. If they think he can tap into the power, it looks like they might get a right-hand hitting Rizzo if everything goes well developmental-wise.