I loved Opaka. She had a warm motherly quality but also a strength of her convictions and a serenity that seemed to fly in the face of the Occupation. It is a shame they never revisited the moon she was on or had more of her in visions and orb experiences, but what little we did get from her was a treat.
With Sisko as Emissary and Opaka being the one who discovered him, you kinda know she would have accepted sharing her role as spiritual leader with him, becoming a mentor and guide to him over time. Which I would have loved to see happen, but in order to make his journey a more difficult one and have another adversary closer to home, they needed another Kai, one who wasn't quite so accepting and was looking out for themselves more than the good of Bajor.
For story fodder and conflict, Winn was a great addition to the recurring characters, well written and acted over the years. Its just a shame she came at the expense of Opaka.