What about a corruption catch up mechanic within one character?
E.g. a global base corruption, that increases with the local corruption. So if I am at 600 corruption in one Monolith and I start at 100 corruption in another I would get bonus corruption from defeating the Shade of Orobyss in the new Monolith.
This way players would still have the agency to keep corruption lower in one mono if they want (via sanctuaries) but would not have to go all the way back to 100 if they are already at 500+ in another monolith.
It's a little different than this but this is already in the game.