For Saurfang, I try to look at him threw the lense of “What happens when an Orc grows old enough to have lived with the crimes committed?”
Saurfang was present for the Genocide of the Draenei, the First, Second and Third Wars, the return to Outland, the war against the Lich King (which claimed his only son), the Cataclysm, a Warchief bent on destroying the world, the return of the old Horde that he had been apart of that had committed Genocide of the Draenei, and the First, Second and Third Wars, the Fall of the Legion and now another War between the Horde and Alliance that would realistically see the loser exterminated.
I’d wager he expected to be long dead in glorious combat decades ago, but here he is, somehow hanging on. It’s apparent he has some level of PTSD (hell, who wouldn’t?) but the way they have written it is not flattering to the character.
As for Baine, I’ve been tossing around the idea that he just simply hates the Horde (or this version of it at the very least). He hates his Father for swearing loyalty to them, he hates Thrall for abandoning them, and he probably hates the Orcs, Goblins and Forsaken for all the damage they do to the planet (The Earth Mother) wherever they go. The Orcs deforest and blow up the land, the Goblins mine, deforest and blow up the land, and the Forsaken simply just Blight it and kill it, almost irreversibly.
In addition to that, the Tauren in general seem to have a better relationship with the Night Elves than any of the Horde races. If not for game play purposes (two faction system and all), Baine and the Tauren are only in the Horde because he values upholding the oath is Father made, whether he agrees with it or not. If not for the fact that this was a two faction game, I feel like the Tauren would have left the Horde after the death of Cairne.