Aye, the recruitment pool faces a lot of potential abuse, but so do crusades. Did you know that crusade armies travel twice as fast, can recruit religious troops (like mercs) and have no upkeep?

No upkeep. Sounds like a dream. But if you don't move the crusade, soldiers will start to desert. But how can you end it? Hopefully not to easy, you can park armies a little too easily this way.