I wouldn't hate adding Kwan, as he is a quality player and has some further years of control.
But if I'm looking to obtain an outfielder at the anticipated cost of prospects, I want at least one of the two aspects: (1) a bat that projects to 20+ HR in a season or (2) a glove that projects to being a starting CF. Of course, having both would be optimal. Perhaps I'm wrong, but I just don't see Kwan meeting either of those.
So then you're looking at having Kwan in LF and Frelick in RF, where neither of the corner outfielders are power bats. (We already have that with Collins in LF and Frelick in RF.) That would seem to do nothing to the lack of power, which seems like the area where the lineup actually needs improvement.