WSG will be tough for sure, but AB is managable with a communicating team. Your boxer roams to support while 2 or 3 stay at each flag, works well, but not in pugs cause no one talks. AV boxers will dominate, with a healer or 2, I could hold off half their team at galv no problem. NEVER underestimate supreme coordination. EOTS is very winninble with boxers, SotA is tough on O, but great on D for boxers (you just man up right at the last gate. Yes, 5 players are better than 1 boxers, BUT, 5 players can never match the coordinated burst of a boxer. And when people die in a global, heals can't do jack.
Plus, having 5 fire elementals out for 2 out of every 5 minutes is a BIG deal. Being able to use abilities like reincarnate and elemental totems is a huge bonus that shamans never enjoyed in arena's.

Don't forget, a lot more people are going to play rated bg's than played arena. Now that they only gain points from winning and can eventually gear up that way, they will play bg's en masse. Yeah you'll get pro teams, but there will be TONS of pug teams and such and I really feel positive about it.