Even if he is a decent pitcher, he is making $10M/year. He is a career 1 WAR pitcher who is having a good year but coming off a bad year. Considering the contract, he is not worth much more than the $4M+ or so they will be paying him.
I assume Elias did his due diligence, made teams aware Cashner was available, and took the best deal he could find. You can't say it's a bad trade unless you can prove there was an offer on the table that was passed up.