NoStageDifficultyScaling

Replaces the per-stage exponential with a time-based exponential scaled to an expected stage completion time.

Old StageFactor calculation: 1.15 ^ StagesCleared

New StageFactor calculation: 1.15 ^ (Time / ExpectedStageClearTime)

Default ExpectedStageClearTime is 7 minutes

• 5 minutes seems to be the expecation of Vanilla, but is unrealistic to how people actually play the game
• Originally tried 6 minutes, but seemed too punishing for stages 4-5 and Mithrix