I don't think its rubber-banding in this case, but there is a sort of anti-agency thing. You have a difficulty curve that a given party can get ahead of or fall behind on. If someone is falling behind, their supervisors shouldn't keep giving them harder and harder duties just based on how long they've been with the organization - that's one way you get dysfunctional organizations (related to the Peter Principle). If the players can't say e.g. 'okay, we're Lv9, but last time we went up against CR 9 foes it felt pretty shaky, lets just do a CR 5 mission this time', then that's a big hit against them being able to be responsible for their own success and failure.