Having been playing FfH only since version .30, I have seen only two different mercenary mechanics, that of the old guild system, and the current one. I would like to suggest a third one that I think might be more equitable to both humans and the AI.
I think that any civ that researches currency should be able to hire mercenaries in any city with a marketplace building in it. The cost of the mercenary should be high, say 250 gold. The benefit of building the Guild of Nine wonder would be to lower the cost by half, and would allow the holder to hire mercenaries in any city, even without a marketplace.
Another suggestion is that the race of the mercenary unit should be randomly given. That would allow for some variation for the troops one gets, and would be thematically appropriate.
Finally, I think that mercenary units should have a small but still real chance of cutting and running. This is after all why states finally ended using mercenary armies, because their loyalty was questionable. Whether in attack, or defense, there should be a small possibility, say 2% per combat, that the unit will simply desert you. Not become a barbarian, but simply get up and go back to whereever they came. That would lessen the appeal of simply buying yourself an army and steamrolling the enemy.
I think that any civ that researches currency should be able to hire mercenaries in any city with a marketplace building in it. The cost of the mercenary should be high, say 250 gold. The benefit of building the Guild of Nine wonder would be to lower the cost by half, and would allow the holder to hire mercenaries in any city, even without a marketplace.
Another suggestion is that the race of the mercenary unit should be randomly given. That would allow for some variation for the troops one gets, and would be thematically appropriate.
Finally, I think that mercenary units should have a small but still real chance of cutting and running. This is after all why states finally ended using mercenary armies, because their loyalty was questionable. Whether in attack, or defense, there should be a small possibility, say 2% per combat, that the unit will simply desert you. Not become a barbarian, but simply get up and go back to whereever they came. That would lessen the appeal of simply buying yourself an army and steamrolling the enemy.