I understand, sympathise and agree with part of what you are saying.
The game has a natural decline in interest it initially generates,generated, and based on personal experience, and what others write on the forum, the updates they keep introducing to keep the enthralled ,does little to nothing for the players at the lower experience levels.
It's making it so much easier for players to wean themselves of playing when there is either so little that they can take part in, or it requires a lot of commitment, and nothing much to show for it in the form of prizes, if and when they do.
I do not see how your idea of moving inactive players somewhere is going to help, for starters it's not a new idea, and though there is a connection,its not really the fact that the kingdom has inactive players that stops your ability to recruit, it's probably that the active players have no reason to join your clan.
Mostly players are not jumping kingdoms to look for a new clan, they already have one in mind.
If inactive players were removed, there might be space for new players to join the kindom, but would they want to be in an old one, and would the active clans want to take on novice players?
I think not.
If you have inactive players in your clan, it ought to be simple enough to just expel them.
However this isn't going to help,and that's because the levels set, are not going to drop, just because you have less players.