Pc-eu.
During the mayhem event, cyrodiil was literally Unplayable.
During your tests cyrodiil is Unplayable. During the high population hours cyrodiil is Unplayable.
Let's take a look on the imperial city:
During the mayhem event, there was over 50v50 zerg combats on almost every district: 0 lag.
When in Imperial city people starts to make ball groups and big zergs to farm bosses: 0 lag.
During high population hours of the day in imperial city there's 0 lag.
Now zos, just ask yourself why. Why Imperial city is so less laggy compared to cyrodiil!?
Now answer this question, not to us, to yourself.
Now apply the answer to cyrodiil, we don't care how, just do it.
We talk, we suggest, we pretend to know how mmorpgs server works, when for real only you know how they really works and how they are coded.
Maybe the solution is so simple, maybe is there! Under the desk! You can do it guys.