The issue is server-side. My friends and I ran multiple traceroutes from locations all across the NA continent, coast to coast, including locations in Canada. Through this process we gathered a plethora of data, and in every single attempt the packets trying to be delivered to the IP address (provided by ZOS themselves) were rejected outright.
In other words, ZOS's servers are rejecting the information our computers (consoles included) are trying to send to them. This is why you get lag spikes and framerates drops, timeouts, etc. Of course, not every issue you will ever see in ESO is due to this, but without getting into a great deal of details that would likely be far more than you'd want to know, every network/connectivity issue I or anyone I know have had is directly attributable to the rejection of packets by ZOS's server(s). They are aware of this issue (I told them, and gave them every ounce of data I gathered over the 3-month period during which I was troubleshooting this), but whether or not they are doing something about it is anyone's guess.