I think the OP has a point, though I think it fails to make a strong enough point. In general, we will group experience systems into one of three groups - Participation based, Individual Event Based(IEB), and Split Battle Event Based(SEB). The current experience system is a participation based system which evenly rewards units for their participation in the battle, regardless of their action. This system gives players a heavy incentive to create the largest parties possible and to prefer small lopsided battles to even or tactically difficult battles. Players who take advantage of the system are not exploiting it, but merely maximizing the systems potential.
If one was to make a change to the experience system, an IEB system would not be preferable. This is the type of system found in games such as Final Fantasy Tactics or Shining Force, where in each individual unit is given experience based on their actions. In an IEB system where actions garnish experience gain, ranged units would have an incredibly experience advantage over melee units, while in an IEB system where kills garnish experience, melee units would have incredible advantages over ranged.
In general, a SEB system is preferable as it is a system in which all experience gaining events are pooled and split evenly amongst participants. In this system, the player is given incentives to fight fair and even matches when attempting to gain experience, while always maintaining a equal experience gain no matter the party size.