If you want players to spread out and stop hyperfocusing individual objectives, you need to make more objectives that can be easily acquired by a small number of players, and there needs to be a huge number of them.
What I am proposing is the addition of flags to a variety of map locations in cyrodiil extending beyond resources and keeps.
Beat a dolmen? Plant your flag until the next anchor drop for campaign bonus points.
Cleared a dungeon? Plant your flag to summon NPC guards outside for a brief period and gain campaign points.
Cleared an imperial camp? Plant flag for NPCs and points
Occupying a village? Occupying a wall? Occupying a church? A destroyed tower? Plant flag for NPC and points!
Etc etc.
Make them repairable too! (For example there is a dead wayshrine in DC territory that could be repaired/occupied to enhance transit and tactical movement)
Captured objectives would show on the map, which would encourage small brawls spread wide across the map.
Take the pressure off of keep battles, and give players something to do when they can't counter zerg.
You could even have mechanics too where players that capture all the keep resources receive NPC seige support as a mechanism for reducing the need for zerging.
Just saying why waste all that beautiful cyrodiil landscaping?