I think there is a problem with multiple Invokers... I could run GR60's in 7-8 minutes average 4 times when solo, and I need 13-14 minutes to complete a GR60 with 4x Crusaders in a team. It's obvious when fighting the boss, it takes so much longer...

So maybe there's only 1 stack on Thorns per target instead of 4, or something like this.