The point of the damage cap?

You're reading it incorrectly, by having duping in the first place, fixing it actually escalates the problem even more if they don't clean it up properly. Aka leftovers. Nexon intended a high cost for those equip's that are presently on the market, instead hackers made it a standard.

Thank you for restating what I said in the "second paragraph" that you probably skimmed over. Hackers made it standard because they duped them, as I said right here "But it also did increase the average standard for damage". How is the problem escalated if Nexon leaves a few leftovers behind but removes mostly everything? A few people have the gear. Big deal. The "average standard for damage" is now lowered. Yes, in your elite circle of friends, maybe a lot of people still have the gear, so it might seem that the "average damage standard" is much higher than the pre-dupe standard. However, average as in, number of hacked equips/number of players, or total "damage/total players, removing most of them got the average much closer to "pre-dupe" standards so everything is much better.

Yes, there are quite a few equips on the market. But haven't you seen that their prices are rising? That's what Nexon wanted anyway - if the duped item's price is getting closer to how much it would cost to legitimately make it, that's good for the game.