I don't think its related to the WoW realm, but rather location in the country.
I tested without my proxy, only Leatrix.
Sylvanas: Home 177ms World 384ms
Twilight's Hammer: Home 177ms World 235ms
Shadowsong: Home 177ms World 209ms
Sylvanas is a full realm, Twilight's Hammer is a medium realm and Shadowsong is low-to-medium realm, and it clearly shows the difference in latencies to World.
Now I see plenty people complaining, 100% of them proving its working fine using their alternative ISP account. So my theory is, it is location based, it might not be that that specific location is having a problem, but rather that location over the Telkom IPC network to Web Africa's IPC links are having a problem. It would explain why there are people constantly complaining, why their alternative ISP accounts are fine (that alternative ISP takes a different route on the Telkom IPC MPLS network) and others are fine on WA.
At least that is what my conclusion is.