Actually, that would be preferable. The higher the gold-power ratio, the more soldiers you'll eventually have to merge with your experts to make it worthwhile. So for high experience units, you would need troops of hundreds of men ready to make that difference count. It would make the training of 8+ units something not too common because the soldiers they'll merge with already have a lot of xp defending unless you're making troops far into peaceful territory.
Ah, I had a similar idea but forgot to add it to my first post. It would be less frustrating if cities and villages would have a small force (f.e. 100 for villages and 300 for cities whose troops have been extracted). This would however require some additional terms to ensure this doesn't shaft the zombies. If they would have to deal with the hour-long countdown before combat, the difficulty would go way down. The zombies simply couldn't spread as fast early-on. So maybe that there is no such countdown if there are only militia involved?
Or make it so that every zombie can only kill so many people. F.e.: One zombie of 12 strenght wanders into a village with 50 civilians. 12 vs 50, the village loses 12 civilians but doesn't fall. But just 5 zombies would do the job of finishing them off. This messes with the lore and thought that just one zombie would need to wander into a village to end it, though it won't happen that often that the zombie strength would be outclassed by the population.
The idea I intended to include was actually mercenaries, 12h or 24h units that can be whipped up as a last resort. Or units that will go out and attack only one target you select(They'll be neutral units), and who'll refuse to attack anything they won't win against.
But militia would work better. For the last suggestion, maybe make the militia thing valour-cost to prevent early-game use.
Men, I know you are scared. You have not received even the basic training that our soldiers got. You don't have the military grade weapons we use to fight the immortals with. You don't even have the time to say goodbye to your families before the undead will be at our doorstep. But you are the only thing standing between us and those zombies. You are the last hope of your family and friends. You are the last stand of this community.