The point of who it helps is not really a big concern in my opinion. At least not in a game as big as G40. If They made the rules to make the defender the strongest, then the two forces would be standing right next to each other. if they made the rules so that the attacker is the strongest, then the two forces would deadzone each other.
there are so many rules and effects that help the attacker or defender, Order or casualties is probably one of the least important. More important include: unit stats, planes cannot land on taken terretory, planes needs carriers or airbases to defend a seazone, retreating gives you an extra round of production in your stack while removing one from your enemy, taking a capitol gives you all of the money, etc…