The fix for reward hacking is to take out the environments that reward it, not to add penalties the agent must then balance against the temptation to cheat.

Like it's a more fragile and scary situation to have agents on the one hand be reinforced to desperately find cheats and hacks and on the other hand try to balance that against desperately trying to avoid negative penalties for like being caught doing these things. You ideally want their training to just not push them in the direction of cheating and hacking in the first place.