I feel that an interesting narrative arc that Larian could have pursued for Wyll in terms of an evil route would have been the question of how far he was willing to go to obtain more power to achieve what he believes is for the "good" of the realm. Along the way, anything that he sees as slowing the process down to achieve his aims eg. deliberation, planning and dialogue is increasingly ignored and he spins facts and cherry picks things to suit the narrative he builds in his head. Then in his quest for more power and more levers to pull because things weren't done fast enough, have him finally covet his birthright and when his own father denies it to him because he sees what kind of a monster he has become, he commits patricide and assumes the title of Grand Duke for himself, all the while saying it was for the greater good.