This is an interesting conundrum, because physical punishment at its most basic level, is ineffective. Restriction of rights is antithetical to what the Korps stands for, so to me, repentance is self-administered, not through brute force, but via the choice to change.
If one commits truly heinous acts, only their victims can provide forgiveness, not some arbitrary reduction of their right to exist, though it can be more complicated than that, given scope. Could a shitty cop could work to being a better person? Prove themselves, their desire for repentance, understanding that they were wrong, and genuinely wanting to work towards something better? That's the bare minimum, but I believe it's possible, and I don't think putting the boots to them is going to magically awaken this within someone.
Getting your ass beat will cause very few revelations beyond: I don't want to have my ass beaten anymore.
For most adversaries the Korps face? They have no regret, so harsher responses are required. Sometimes there is no saving them. Some folks? They don't want to change.
I don't speak for the entirety of the Korps obviously, these are just my thoughts on the subject, but who doesn't love a good redemption arc?
