On the Agatha front, her understanding of the Darkhold and its history might have prevented her from reading as much as Wanda. Or the shtick of "absolute power corrupts absolutely."
Now if* anything positive is to come of the leaks it's that many have claimed she is essentially the second lead, with considerable screentime in the film; while that can definitely be a negative for people (i.e. more of a chance to butcher her character), I often think "villains" and their motivations seeming lacklustre in MCU fare is often a consequence of being underwritten. Wanda will at least have her library of limited MCU movies and WandaVision to supplement her story in addition to secondary lead screentime in MoM - which could add up to a more convincing, compelling, and emotionally resonant story for her. I would have preferred for them not to double-down on her trauma, but I'll make something I can drink outta the sour grapes they've given us.