The trade makes no sense, however you cut it. We aren't going to replace Erden with a better player
I think that depends on how you view Erden. While I was impressed with him, I think there are a lot of guys who are big upgrades over him for the playoff run this year (Murphy is certainly one of them).
Honestly, I just did not feel comfortable with having him play during the playoffs this year, even in case of an emergency.
Where it is a loss however, is in the future. As he gains some weight, I think he will get better, and should be a quality rotation big man, and will likely gain value in the next couple of years.
I did hear somewhere however that he wants to return to Turkey next year, both because of the money, and because he is homesick. And while I have no idea if it is true, that would make this deal make a lot more sense from a value standpoint.