Looking at Roy's fight with the DJ Assassin, if that dude is considered to be an "Average" member of the LOA, then Team Arrow really doesn't have much of a chance on taking on even a handful of the League members.
Heck, even with a combined assault from Oliver and Malcolm, I bet that the most that they'll be able to do is just keep Ra's busy for awhile.
But Laurel (at her current level of training) along with Roy and Diggs wouldn't be able to take on most of the League members, especially with Nyssa leading them.
I would imagine that if Ray joins in the fight with his Atom suit that he'll be able to make somewhat of a difference.