Reading TWOK again I think Brandon is being clever by providing unreliable narrators of the events. By using different persepctives he can portray different parts of a person in a way he couldnt otherwise. If we had seen dalinar as he was originally odds are readers wouldnt give him the same grace they do when they learn of his past. We learn of the conquest days gavilar was a man as cunning and cruel as sadeus and as terrible nearly as dalinar. We learn later that he had connections to terevangium, and the sons of honor, and thta he knew something of the radiants and the everstorm. We learn early on he wants to take being king to the next step and become essentially a God through surgebinding and oaths. Lastly we discover he was an abusive husband, emotionally and verbally if not physically. Combined these things make a lot of people feel he is as some people have put it a "cremstain".
But we also read in TWOK that he started to change near the end. That he listened to the way of kings, started to ask what the point of war was if his people couldnt eat. To urge his brother to keep the alethi codes of war. etc. He received Honors visions of what was to come and I think it would not be unfair to suggest that maybe, just maybe he could have taken the same path dalinar took. His initial goals were all selfish and his actions in many instances evil, but in many ways so were dalinars. The fact that Odium likely manipulated gavilar doesnt change this, after all odium tried the same on dalinar.
I think there is a non zero possibility that gavilar like dalinar or in part like elokhar could have been on the road to a redemption arc, the very nature of the radiant ideals sort of pushes that direction anyway, but as we learn more its also certain that gavilar at the end was not yet anywhere near where we see dalinar in the way of kings, nor yet where elokhar was when he was last seen. As we learn more though it is possible that he really was just a saddeus + amaram + dalinar mash up, which would probably be the worst case scenario for the character suggesting that Dalinar and Elokhar simply remembered him with rose tinted glasses.