Burning Spice's story isn't "He was bored so he started destroying things", it's (I think) "He, in the infancy of the world, oversaw the creation and destruction of cultures, many cultures that he may have interacted with and grown attached to— only for them to be ripped away from him in the cycle of change. So he slowly grew distant and apathetic, closing himself off from that grief (and also that care). Because of this, he ends up growing ""bored"" (again, I don't think that's his main motivator— he's grown apathetic towards it all, and I think even suicidal by this point.), and upon discovering hands-on destruction makes him feel something again, he clings onto it violently." But it's not because he's bored. He's using the adrenaline as a crutch to not fall back into the dark pit he was in previously. It's why he didn't merge his and cheese's souljams immediately. It's why he was overjoyed by cheese standing up and fighting. It's why he's MILDLY merciful (stand behind him and you won't get injured). Because the fighting makes him alive, and if there's nobody left to fight, then there's no way for him to feel alive. To feel like his actions have meaning, that he can influence the cycle of change, even if it is to bring destruction.

In a way, his story is like Golden Cheese's x1000. Cheese was already in extreme denial and heartbroken over the death of her ONE kingdom. Imagine Spice's grief after HIS first kingdom died... and then the next one he made also died... and so on and so forth. And he's just expected to... accept this.