Will Queen Zeal it's hard because we never really saw her character before influenced by lavos. I think that in her case it's both corruption by lavos, but also just her succumbing to her worst possible instincts. As far as I know the earthbound were never exactly treated well, even before lavos was discovered. So there is a good chance she was always capable of horrible things, but lavos drove her further into insanity and made those traits the sole defining thing.
But yeah, she might have been the nicest queen ever before lavos, and maybe a hope for reforming things. But it's really hard to say. The only real sources in game all point to her regime becoming more authoritarian, starting after the death of the king and escalating dramatically around the time lavos was discovered. But it seemed that authoritarian streak was always there to an extent...