From my modding experience, AI doesn't seem to prefer 0-turn units, and 2-turn isn't enough to affect AI's campaign decisions. Usually they schedule 2 or 3 units into queue, so 0-turn does have the expected effect to speed up recruitment, but not much else.
Generally, AI prefer elite units over the levies if they can afford, unless during emergency situation. If recruitment zone is not counted, it's not uncommon for a rich faction in 200-300 turns to have dozens of elite armies and almost no regular ones, even if each of the elite unit may take 2 or 3 turns to recruit.
What the turns really have effect on is the capability to replenish. If the elite units are destroyed and the enemy is pushing deeper and deeper, AI would begin to get mercenaries and cheaper units. But it still wouldn't prefer 0-turn ones unless they're good enough in their class. Also the 3-unit queue limit remains - so it'd be at most 3 levy units per turn, or 2 levies plus 1 regular unit.
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