I recently faced a few people who had miner cities by the time I launch an offense. The most recent one I faced started with a spearton. I beat that, took the center. Waited a bit to add a few swordwrath and speartons to my army. I had about a line and a half of troops, no counter-offense to be seen. So I decide to attack and I see 20+ miners getting gold and mana and I see a fully grown giant walk out of the castle. I decide to retreat. Eventually giants kept coming and he took the tower. As soon as he takes it, a ghost giant comes out of the center tower.
I basically lost at that point.
So my question is: Is a miner city really that effective that consistently, or should I launch my attacks sooner? Or maybe should I consider miner spam?