Could be your internet. I have insane internet and i don't lag ever. The only time i feel the lag is when an alliance is capturing a flag with a huge Zerg. Other then that, it's pretty good.
Also, IC DLC is said to have a huge impact on PVP performance in a good way. Something to do with all the check's skill's do within radius blah blah blah. All i know is we are going to see improvement's.
There are countless reasons why there could be lag. Unless you can actually pinpoint what is causing it, then you can't exactly just blame it all on ZOS.
The more and more players you have that level up (getting a wider variety of skills and effects) and get in the habit of using other things like seige more often and group up more, the more lag you will get. On PC lag has only gotten worse and worse every time since launch (even with their attempts to improve it).
A lot of players assume it's one or two specific skills that cause it, it's not. They just add to it along with every other skill that requires tons of checks with their servers. Combined with how many checks there are per player just for being in a group, there is no doubt in my mind a lot of the problem comes with large groups straining the server as well (cap group size at 12 zos and clean up some of your checks).
They are removing one of the Light of Sight checks with next patch, which might help some, though probably won't fix it all.