I just started a game with Ceresa, I finally got the Dirge of Ceresa spell and it is super powerful. I even forgot about Corruption. Now that I have done that, it is almost a one shot kill for everybody. I annihalted the Altar Kingdom by just walking Ceresa by herself from city to city. The Champions that I fought in the first battle, which I did have some help, were all hurt. So the spell even killed all of them.
Now, I have started casting corruption, and it is just brutal.
I think bonuses to Dirge, and things like the Pyre Sword need to be based on combination of Shards. For every death + fire share you get the bonus. Not just death or fire. Dirge could be Death and Water combination. I also think it needs to be a higher level. It the lay out worked just perfect and I got Ceresa up in level pretty quick. I only had to champions and they were both Governors so I left them at home. Ceresa is practically untouchable right now.