I would say your first problem is expecting perfection. Everyone that plays this game is human and therefore not perfect. Peyton Manning does not complete 100% of his passes, Lebron James does not make 100% of his shots. In a video game, why would you expect people to never make a mistake?

IMO, when your putting 8 randoms in a group together, no matter how skilled, it may take some wipes for the team to gel. Once it gels, then you can get repeated kills. In a perfect world, yeah, a farm group in PF should be able to kill it on the first try. This is reality. Wipes will happen, people need to accept that. Rage quitting after one or two tries is the biggest problem with group stuff in this game.