After a years worth of constant forum posts and customer service calls i've given up. I highly doubt that ZOS will be able to "fix" the lag. So far the only thing "unlimited" about Tamriel unlimited, is the Lag.
Of course, they promise hundreds of players on screen at once, in epic pvp battles...
In Thornblade NA you get 5 players on screen at once and its slide show city, but go to Blackwater Blade NA and there is virtually zero lag, and yes, hundreds of players on screen at once with no problems.
Either the problem lies within the VET version of PvP, or they have Non-Vet PvP souped as a façade, to lure players into staying.