As you know, Skirmish risk/reward ratio isn't right. They need to develop a more balanced way for it. I suggest what follows:
1- attack level limits
K1 is allowed to attack up to K5.
K5 can attack up to K1- K10.
K10 can attack up to K5 - K15
2- Open players levels limit:
Any player can attack any other players but when attack lower levels, fewer pearls he can get. And vice versa.
This rule applies to all players in the coalition. Of the victim of low level, the higher level players in the coalition get fewer pearls. And the numbers of kills still applies too.
3- increase the protection level for both the attackers and the defenders. People won't defend if the need millions of resources to recover the loss.