Well, most of it is airdrop too but still
So taking your numbers, and saying that airdropped merits were 10/100/250/500/1000 for ranks Member through Legendary, the amount of airdropped merit destroyed is
(10*150)+(100*93)+(250*30)+(500*8)+(1000*1) = 23300
So, we have actually only destroyed about 1.2k earned merit. Yes, that's a lot of airdropped merit to lose, but honestly, I don't see that as a problem if the users are deserving of their ban.