I think the Nats did very well in this deal. No serious valuation of Eaton could lead to any other conclusion than the Nats easily "won" this deal.
Eaton probably has a surplus value of $150M or more. Giolito is probably worth $70M, Lopez $30M, and Dunning less than $10M.
Robles ($75M) plus Giolito would have been much closer to "fair". Personally, I was ignorant to just how good Eaton has been and projects to be for quite some time, as well as how cheap his contract is for the next 5 years.