Ball groups spam of abilities creates extremely high latency in a small area because such spam simply overwhelms server processing queue.
This results in many unfair effects for other players such as:
- GCD about 2-3 seconds
- inability to break-free in 9/10 cases
- stun-locking / multi-stunning thorough break-free-immunity
- unwanted latency teleportation
- large sound delays making ball group attacks muted and therefore stealthy

Cyrodiil is already barely handling large scale battles of non-grouped players while the advertised point of Cyrodiil are large scale battles.
Ball groups come in knowing very well they are solely based on exploitation of poor game server processing.
This massive and highly concentrated spam simply creates forced server processing priority for the ball groups.

Countless people leave PvP all together or take half-year / year pauses from the game just because of this.
Also from the business standpoint, these players obviously don't pay when they are gone.

10 years of the game and here we are with the one and the same problem... abuse of game engine and network structure.