they brought in the wrong rookie- Cora and Boone were both fine
The Yankees and Red Sox were objectively better than the Nats. And their success doesn't change the fact that rookies are more likely to not do well than experienced managers. You are rolling the dice. It worked out for Boston and New York, it didn't for the Nats. Kapler's team collapsed at the end. Like not even competitive.
And it's not like the Nats wouldn't have taken Cora if they could... They got a rookie that was bottom of the barrel after everyone had gotten their pick.