I don't know how it works and I doubt anyone that does know is going to say on here at all. But how is it extreme? There is a bug that allows duping of items using charmed mobs, unless the bug can be fixed the logical and reasonable solution is to remove charm. Otherwise you end up with a server destroyed instead of a server with no charm.
I think it's extreme because it takes away a class defining ability, and I'd wager that others agree since barely anyone is playing a chanter on this server.
How about making select non-quest NPCs charmable instead of making all NPCs immune to charm? For example... make the giants in BOT charmable, and trash in Dulak, PoTime and Qvic, etc. Keep all else immune if it's too much work to reactivate charm server-wide and cherry pick NPCs for immunity.