It is all about the skimish links. If the smaller gang has more range and speed, they can succeed against a larger force's lighter faster ships while avoiding the rest, even if they're originally the same hulls. Only the armour and shield tanking links scale in a more direct manner, positioning doesn't.
Actually in Tarm's direct comparison, with the >2x effective RR from maxed links, a 1 OGB is in some ways at parity already with just 1 RR fielded (not considering the 1 logi being shot/jammed), and with more than that, they half the number of pilots that need to be in logi ships to provide x RR, thus allowing the smaller gang to bring more dps/tackle/whatever without tradeoff. They don't even need to be pilots that are able to fly logi either, so the OGB's SP help out gangs of newer pilots more.