I think you're underestamating Whitebeard and his Crew... don't think just because Luffy and his Crew are the main charachters that they are the only or better yet Strongest.
Well Boa doesn't HAVE TO FIGHT Luffy. I mean hes one out of the 'thousands' of pirates that came to repel Whitebeards invasion. I'm sure she could easily avoid conflict with him. As for Gold Roggers son... they just pulled that one out of their ass IMO.
Well as shown in the new chapter it is obvious that some of the Shichibukai don't even give a shit about the war between WhiteBeard and WG seeing how utterly powerful Whitebeard is. However it is notable that none of the seven Shichibukai can stand a chance , well most of them can't stand a chance against some of the captains of Whitebeard pirates seeing how easy it was for one of the captains to deflect the sword slash from Hawkeyes.
And I didn't mention this but could it be possible that Boa can just fake her death or something to be neutral to both sides?
The battle reminds me of the final battle in X men 3 ONLY ON STEROIDS!