In order to reach a stable equilibrium, it must be easier to defend than to attack. otherwise, as soon as contact is made, the two players are going to rush each other and the game ends immediately, and I think most people don't want that kind of game.
And yet the defender has very little benefits in this game. the situation is made worst by the new trunk, where the attacker can handpick the attacking soldiers - meaning he can choose to let woounded soldiers stay to heal, while the defender won't be able to do that. with that change, I think attacker has full advantage, and there simply is no sound strategic reason for at least one player to not attack as soon as possible.
So I think, to promote stability we should give some help to the defender. Not really sure about what, though.
One possible way is to give a slight power bonus to soldiers ffighting in their borders. I don't really like that much, though.
I propose letting soldiers heal inside their borders even when outside military buildings. THe major problem for defender is that most soldiers will rush out to face an attack, and will not heal while they are there. So by attacking with one soldier at a time it is possible to stop a player from healing most of its soldiers. If those soldiers could heal at a slow rate even while outside a military building, that would help compensate this disadvantage.
Another problem related to defence is that you have no control over the soldiers that come out. Sometimes the rookies go out, leaving your hero inside to gather dust. Sometimes your heroes come out leaving the rookie behind, and you lose a castle to the lone enemy soldier that manage to walk to it. To fix that, we could give the player the chance to select which soldier will always stay inside until the enemy knocks at the door. it could be selected for any military building.
regardless of what you think of those proposals, I think we need to find some small advantage to give the defender so that the game will revolve in an economical challlenge instead of a rush.