As I mentioned in the first post, I used 2 swords & 2 catapults to take down 3 pop city & a garrisoned slinger. Still I lost one sword & the other was badly damaged. So healing is definitely fast especially in early stages when you can't field a very big force & catapults already do little damage to cities.I don't know. I think the healing is OK and you really shouldn't be able to take a large city with less than two siege units. Maybe it should scale more with city size or siege units should get a new bonus that slows down city healing.