There are 3 core problems which very negatively affect ESO's PvP, always have, and have always been readily solvable.
1: Three teams.
This absolutely ruins the majority of PvP experiences in ways players may fail to recognize. In Objective BGs, two teams will usually get locked into fighting each other while the third team plays the objective and wins the game, which then feels disappointing due to the fact that there was little to no PvP actually occurring for them; so everyone loses one way or another, and it feels bad. In chaosball specifically we see one team hold the ball at their base while the other two teams bottleneck into each other repeatedly, often failing to reach the winning team altogether. In deathmatch BGs, the issue of team focus is still present, but we also have the kill steal issue, wherein a player with an execute and bloodthirst jewelry simply steals kills from each enemy team using either the sorcerer or templar ranged executes. Winning this way does not represent the ESO PvP action combat process very well, and losing to this feels pretty bad because you likely put work in and someone else got the credit.
SOLUTION: Simply make BGs a two team PvP setting like it should always have been.
2: Snowballing.
This is a huge flaw of Cyrodiil. Whichever alliance has the most members on at any given time of day IS the winning alliance during that time. Attempts to defend versus being outnumbered rarely has any meaningful impact (for the average player, never mind the 1vX overlords and their youtube videos). This discourages the losing alliances from playing, and we see most log off, resulting in even greater difference in number of members between the winning and losing alliances. Then, the winning alliance gets a large amount of buffs; they get emporer, they get all the buffs for owning all the keeps and scrolls, and they can control hammer. All this results in a putrid experience the absolute majority of the time, wherein one alliance "takes the map", gets bored, logs of, and the process rotates through the alliances. Most of the time spent in Cyrodiil is spent fighting guards....
SOLUTION: Simply convert keep and scroll ownership buffs into debuffs, and add a gradual debuff element per member active on your alliance so as to even things out. The benefit of owning keeps and scrolls should be the points they give for the purpose of winning the campaign, and holding them should be more challenging the more you have, not less.... Notably, the low population bonus currently in game does nothing to help the issue as it is a point multiplier for keeps/scrolls/resources which you likely will not own....
3: Cross Gosh Darned Healing.
We all know.... This sucks donkey droppings! How many deathmatch BGs have YOU played wherein all three teams had a healer and so by the end of it the round times out and the score is something like 30/15/45....
SOLUTION: The absolute solution to this is actually pretty complex, since the issue involves more than we readily perceive, and I am keeping that to myself as I doubt it would be accepted into the ESO community (it would be a huge change). But alas! There is a simple solution that ALLEVIATES the problem well enough, and we all know what it is. -50% healing/shielding from other players slapped into battle spirit. Done!
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Guaranteed, the day we see these changes is the day we see a surge in PvP activity and satisfaction!