Speed was now of the essence for the party. They knew that the war between slimes and the angels was growing. While it was not necessarily a war so to speak, it was one of sorts.
A battle that was the prerequisite to a war that is already under way. The party, and Genesis, wanted to take down the demon king, the one causing all the issues that they had to handle right now. Especially since he was clearly allowing more problems to happen.
Envy, the slime breeder, acting out was definitely because he had gained more strength. Definitely because he was no longer being held back to gather materials or certain pieces of intelligence for the demon king.
