It is true that most of the big unions use exploits of some kind, generally the abuse of multiple windows to farm several different demons at the same time and to have reduced BP costs. Players that do this can easily be identified atm, by having an excess of 50 - 60+ million PP by the end of the union raid. Later on that becomes easily achieveable, but not right now.
I think the highest I've ever gotten was 40 million with my best team and a very high (120%) assault bonus. That required no-lifing the event. Constantly checking the game and manually soloing high level demons. The reason I farmed so hard was because there was money involved as our own union rewards.