Oakland fell apart due to a team wide slump - some of it might have been regression. Cespedes was a .300 OBP guy, which while the power is nice, that's generally a guy not doing his job. Offensive value is pretty straightforward - outs are bad, everything else is better. Occasionally outs are ok, but those are cases where the second run doesn't matter.
As far as Rivera goes - he is the greatest 1-inning closer of all time. The way the gig has evolved over time, he is the best at the current version of it. Now do I think the gig which Rich Gossage or Mike Marshall had in days of yore was fundamentally more challenging? Yes. But that is a non-issue here. Rivera's brilliance proves his brilliance, not the general level of the gig. Joel Hanrahan and Fernando Rodney explain more about modern closing as a gig than Rivera or 2013 Uehara do.