1. Alliance points for the entire faction, tired of let us say the opposite faction having 80K points and yours having 30k points, add a max cap to how much far one faction can get ahead of maybe like 5K, so if highest score of second highest Alliance is let us say 40K then the highest ranking alliance.. would be able to max go ahead by 5k points so 45K making the competetion more tight.
2. Alts of yours in another alliance cannot be in the same Campaign as any of your other characters, this avoiding taking over keeps without having to siege at first, or at least reducing it.
3. The bottom Alliance, would get increased alliance points to be able to keep up better so it is not just a lost cause and still having a chance to turn the tides if it get better later on, keeping goals and competetion up, eg. like in suggestion 1. but just being at least -5k from the middle Alliance of all time, keeping the pace going.
4. Have a look at the lag beast and maybe learn from eg. what they did in EvE Online which we know is a megaserver game that handles really well, have to say though that ESO is handling massive amounts of people in pvp well though, but hit the last edge to make it even better would be nice.
5. I don't think either Alliance is too powerfull, it often seem like it, players in between encourage your alliances to work better together... there is so many dumb ways to die and fun too lol.
6. Maybe have a Cyrodiil for lowbies let us say from level 10 to 40 to be in PvP with people in that range only having a few set campaigns for it or something, 41+ would be in the real PvP Cyrodiil Camoaigns encountering everything from level 41 to Vr10.


And Finally some entertainment - From Portal -Dumb Ways to Die-
https://www.youtube.com/watch?v=-SSdTXNK2mo

Ps.
Pleace add on more suggestions if have any, in this post, look away from class issues and class balance, but merely look into what would make pvp fun on the current build as it is now.