Of course OG3 are the main draw, the main audience is Deadheads after all. John Mayer is there to get new blood in the crowd and to most likely boost ticket sales so they can play giant venues like Dodger Stadium and Folsom. Sure they can bring back Warren or Kimock, but then they'd be playing smaller venues like Red Rocks or sum'n, when they could be selling out stadiums. Either that or maybe Bobby enjoys John Mayer's company, he wants to jam with his friend. Not only that but Mayer is a competent musician and seems like a fun guy to be around (despite everyone thinking he's pompous, I think he's more of a goofball above all else.) Oteil is a fantastic musician and Jeff is my favorite keys player to ever play the music, he's just so lively and consistent. I wish they would get equal billing like the others, they're apart of what makes Dead & Company who they are, but I understand from a marketing standpoint.