This is where I don't think the "drop him immediately" view is accurate. Players aren't stupid (well, kinda). If the club offers someone five million bucks then drop him the next week it's pretty obvious that they didn't suddenly decide he's not up to first grade. If he was the best 5/8 at the club last weekend he still will be next weekend.
Think of it from a player's perspective. They're busting a gut to win now, why would they be anything but pissed off if the club - in their eyes - made that less likely by dropping the best option in a position (and one the club clearly also rates as it just offered him a big contract)?
As I say, the complicating factor is Fainu because he offers a similar profile to Galvin - talented but raw, basically - and it might help offset the disquiet in the squad thing that he's got two brothers there. On the other hand, it might split the dressing room down the middle. If Fainu wasn't there I'd 100% be saying dropping Galvin would be a dumb idea.
As it is, it's more complicated: as I say, I don't envy Benji. And just to be clear, I definitely think the optimal outcome from this season is more game time for Fainu and less for Galvin than I thought a week ago. It's just not black and white.