Is this problem a hardware problem?
Can a decrease in connection drop the lag (read here instead free to play a 30 day free to try?
What will happen if you nerf twf and then your base increases 500%? What will you nerf later?
Can you reduce mobs and foes calculations and leave players alone?
if you eliminate trade and advice will this help?
What if you reduce attack speed overall, players and foes?
What if you limit raids to lets say 9 or 10 players?
What if you implement single weapon stlye feats giving choices to new viable builds? less twf toons less lag
But I got to ask , Is this really a hardware problem? Did your base increased in a unforeseen way that your hardware improvement budget fell short?