This is an interesting situation. Brown is arguably an upgrade over Amari --so, currently speaking--The Raiders swapped a 3rd and a 5th for a 1st round pick and arguably got a better player, at least in the short run.
Brown will not likely play out his contract and it is going to cause one hell of load of dead money if he doesn't play it out. Plus AB is a locker room cancer. I don't see how he ends up being happy playing for the Raiders as a team in transition.
Here's the interesting part. Why would the Raiders trade Cooper and end up paying even more for a much older, problematic player? They have enough picks to stockpile some talent, but by the time that talent matures AB may be done.
I just don't understand the Raider's thought process on this one. Cooper is young enough that he can play out a new deal and he seems like a quiet, unassuming player. About the only thing that makes sense is that maybe the Raiders knew Amari would not resign and they wanted to move on before that happened. But that seems a bit of a stretch to me.