In fairness to the game about the whole Kagha thing, Arabella tried to steal a sacred, religious artifact. But yeah, the amount of care the game devotes to that, compared to the brothers being killed is quite a divergence, especially considering the hullabaloo was going on before the child died, and there's a whole moral debate about it. And Kagha imprisoning the child would always only have been a temporary measure anyway until the tieflings inevitably left. I agree that death is an overblown punishment for sure, but I think being kept locked up for what realistically would have ended up being a couple days whether our group had come around or not, is actually fairly reasonable.
On a brief tangent from that, I think if they wanted to sell Kagha's eventual possible redemption, they shouldn't have had her be so firmly cold if Arabella died. Have it be that she never intended for her snake to strike but it acted out of instinct. Show her faltering, show that the situation escalated farther than she wanted, but then have her double down to basically save face and present what she thinks is strong leadership. And if Larian really wanted to make her redemption feel more real, then they could have made it so that, if Arabella did die and you've exposed the shadow druid plot, you can use that death to leverage her conscious and make it easier to get her to turn. In general Larian should have shown her armor cracking once or twice to better sell a redemption.
