Leske betraying Brosca was a little hard for him, so he went through a small change after killing his childhood/best friend. Only reason he didn't become fully ruthless was because of Wynne, Leliana, Dog, and his family.
That scene was probably one of the most painful I remember it really made my warden feel like a character in the world rather than a player stand in, the commoner was my favorite origin. I RPed my dwarf as the opposite of yours apparently, he started off ruthless and became nicer over the journey. But killing leske was a big epiphany for him, he realized that leske was right, if their positions were reversed he would have tried to kill him too and decided to never be that person again, becoming much more forgiving and heroic (which opened up a whole other can of worms when this change led him to spare loghain).
Also morrigan and my Brosca just fit to me, both are outsiders to their people, both have troubled relationships with their mothers, both were pragmatic, it all just seem to parallel each other. I also like that morrigan, regardless of your relationship or lack thereof, will jokingly mention that Brosca and her have a lot in common if you take her with you for your first conversation with your mother when you return to orzammar