First, please read
https://ashesofcreation.wiki/Player_corruption. The overall philosophy is summed up by this:
There is no incentive to go corrupt... There's zero incentive for a player to go red. It actually gives you negatives for doing that- very significant downsides. – Steven Sharif
Based on a post by
@NiKr here:
https://forums.ashesofcreation.com/discussion/comment/449170#Comment_449170
True, but it could be one 10-12s mob that removes 30/100 corruption instead of two 6s mobs that each remove 15/100.
It dawned on me that we have VERY, VERY different ideas of how hard it should be to get rid of corruption.

Using Nikr's numbers at face value, that's 7 mobs that take six seconds each to get rid of corruption, or 42 seconds + time between pulls. He later clarified with this, which is less insane to me:

My preferred balancing for corruption gain/removal is "if your first PK was on an equally-leveled opponent deep in a dungeon - removing it should take just a bit longer than it would take that person to come back to that location"
And it would go somewhat exponentially upwards from there.
My Take
I would like to see it based on
death penalty XP debt amount, and then modified by the
PK value of the player, and of course the level difference of the killer and the target.
The death penalties for corrupted players are 4x that of a non-combatant, and based on the 3-4% xp debt given to a non-combatant upon death, it sounds reasonable to me that you need 4x 3-4% XP of any given level to grind away your corruption before any other modifiers. I'll just round it to 15% for the sake of simplicity.
The only quick way to get rid of corruption should be from dying. 1 death is fine for the first kill on an equal levelled player with 0 PK value. That gives around the target 15% xp in the form of debt. Adding in a high PK value and ganking a lower level player, it should require 2, 3 or even more deaths to get rid of corruption, with 15% xp debt accrued each time of course.
Another important factor to remember is the
bounty hunting system. Corruption has to last long enough that Bounty Hunters have time to see you on the world map and get there in time with some friends, and we don't have much fast travel in the game.
So how long does 15% xp translate to? It'll depend on the level, but if we go with the 225 hour to max level goal that Intrepid has put out, that's 4.5 hours per level, or around 40 minutes for 15% XP. With the usual levelling speed curve we see in MMORPGs, that's probably a minute at lvl 1 and an hour or more of grinding XP at level 50.
Edit: And of course we have to test it, but the 15% XP is a good starter I think. Maybe we end up with 10% as a more fair target. We'll see.