Here are a couple more arguments which I don't necessarily believe, but am willing to ponder.
When Giordano was paired with TJ Brodie, they were one of the best pairings in the league. When Giordano was paired with Deryk Engelland, they were effective. When Giordano is paired with Dougie Hamilton, they are one of the the best pairings in the league. The common theme there is Gio, and another common theme is that each of those three guys were less effective on other pairings than they look with Giordano.
What if Haninin is just as good a defenceman as Hamilton, but just doesn't have the opportunity to play with Giordano? In that case, we'd be essentially getting a RW without downgrading anything.
Also, trading away a RHD means Andersson has a spot to win, and he seems more than ready.