Current state of things is that the game - at level 30 with reasonably upgraded gear - is extremely easy. Like ZZZ easy, compared to any freshly rolled character going through the story from the beginning.
As we already have “burn stuff in campfire” mechanic, it could be easily reused to provide the following:
- until we reach the initial plague threshold, scale the area level up to 30 when burning in campfire
- after the initial threshold is reached, the rest works as normally - adding corruptions and boosting intensity
As a bonus it also automatically guarantees that the basic plague outbreak will always be level 30 - as it seriously should be.