Yeah, but it affects ALL charisma rolls, so it's effectively just a permanent CHA boost applied directly to the character. No functional difference from naturally high CHA, IMO.

Wait.

It doesn't work if target doesn't have LOS, so loophole found, we just have to invent the internet or telephone in-universe to nullify sokka's advantage.

Edit: or drop a permanent orb of darkness over him so nobody can see what he looks like