This is a major problem for all parties who group exp with a tank.
https://www.youtube.com/watch?v=CkeT6s6uYj4
As you can see, on this video if you attack a group of mobs with mass target spell, only 1 mob will come and attack you.
On l2 scripts that is not the case, if you hit a group with a mass target spell, several mobs will attack you.
https://www.twitch.tv/videos/164867967 37:53
please look into this as soon as possible