thats not a problem of 1.5 patch, afaik on club there were 2 parties killing most of the bosses, was uchihas pt vs demon(dimon? idk, some russian guy) pt, we fought for a lot of bosses, it wasnt particulary good xp or anything, not like you could abuse it much, because there is not much xp boost, bosses are spread around the map, they have too big respawn and there are very few of them after lvl ~60 (i think highest is rahha at 65 lvl, which was impossible to kill unless you bug minions)
problem started to be with too many stackable bonuses in later chronicles and the moment they introduced 21h bosses, which spawned 6-7 bosses on high lvl range (75/80) at same time next to each other and some side dominated those, hopefully they wont introduce them with the update of server, even if there are no xp boosts, coz xp from those bosses was just too insane
i still remember those fights where you pulled boss to narnia and the enemy pt still found you if they knew the boss is alive, you got these kind of pvps for arak on skylancer hill or fight for rahha at westland