Dear Customer,

Thank you for your reply.
We are aware of the concern of a number of players regarding performance issues during some sieges.
We are constantly working on improving server stability and performance and we are in the process of collecting more information regarding this issue.
We would like to apologize for the lack of communication regarding this matter through our official forums.
We will be placing this ticket 'In progress' until further information is required or we have an update for you regarding this matter.

Thank you for your patience and understanding while we work toward improving the game's performance and experience.

Regards,
Customer Support

So they don't have a clue.