Looting has become more prominent as a method of warfare because of the estate system. Denying regions is a better way to win a war than to try and take them all with your already abysmal land-to-nobles ratio. There's no need to rebalance this as the new estate system should do a lot to help turn the tide and bring us back to the good old days - where wars were nearly always fought for land, as novel as that sounds!
It's also harsh, I think, to blame the mechanics. The estate system aside, the game doesn't force anyone to loot. Yes it's effective, but once you start looting with impunity, your enemies start doing it too. That's the risk you take. Really a lot of realms ought to be more gentlemanly in their warfare, because when all's said and done, both sides want to come out of the war strong and intact, without the prospect of prolonged, eye-wateringly dull efforts to restore battered regions. And what's fun about camping a big army in a region to loot, being constantly interrupted by peasants (though that changed recently?) and avoiding open-battle? It's so boring.
For me this doesn't need changing, the primary suspect in the growth of looting is about to die a death with the stable update. Couple that with migration now being able to revive ravaged populaces much more easily and I'm happy enough with that.
