I'd not call it that, it is a very evil choice, after all. Rather, my impression of Gale is that his moral compass is flexible when it comes to gaining power. In this case, Sharran support and favor.
That's why I wrote that it seems specific used for general. It makes sense for a Gale who is anti-Mystra and pro Ascension, especially since in Act 2 he seems very interested in Sharran shadow magic but Mystra's orders keep him from trying it - unless the player pushes him. It makes less sense for a Gale who is on the road to redemption with his goddess and wants to be freed from the orb (with the implication of becoming a Chosen again in some dialogue) for the same reason, Shar alignment seems like shooting himself in the foot in that setting. He was previously always a bit nervous around Sharran things when having a pro-Mystra attitude in Act 1 & 2, this seems to be missing from the "our loss our gain" comment too, which is odd.
Otherwise yes, I mean his comment for Astarion not ascending is along the lines of that it was better for his soul, but the power would have been nice.
