I take it you have never taken a city with autoheal bots running. I have. Used over 1 million troops to capture a city with 300k in it and apart from towers this city had no wall defenses (traps/abs).

Even without traps and abs, a well layered city will be extremely hard to penetrate. Take a city with 300k warrs 50k pikes & swords and 200k archers. Layered cav/phrax waves will not penetrate that. It would cost someone almost 2 weeks of troops on maximum build speed to take such a city.

How long do you think cataphrax take to build in Age 2 with a end game hero? You are looking at close to a week to build 100k of them. As I stated, the expense (timewise) to take a well fortified city is not worth it.