High pings are not necessarily be because of network latency. High loads on both the client and server can also result in high ping values.
The lag we complain about when there's 3 raids stacked is not network latency. It is primarily because the server is at maximum load or is experiencing some kind of bottleneck. Though some will also experience client issues under those conditions; for example, when a zerg arrives in the area you're in and causes your client to briefly freeze or stutter while it processes the art assets used by the incoming characters -- this may also increase your ping as your client was unresponsive for a few moments.
Of course, it can also be reflective of network latency when there are issues such as router problems or ddos attacks, but in the case of PC/NA, this seems to be infrequent.