I'm going to have to disagree with you on this. Early game, Civ 6 cities aren't hard to capture. But late game they are next to impossible. Case in point, I have a game where three armies of infantry attack a city with 99 defense (pretty standard defense rating playing on Emperor). All three armies took 75% damage and did a combined -18 damage to the cities defenses. Three armies of infantry. Of course next round all three armies are insta-killed by the cities counterattack which conveniently regenerate 15 defenses. So the effective attrition rate is -1 city defense per attacking army of infantry. And before you roll your eyes and claim "muh artillery stupid!!!", I would like to point out a single volley of armied-up artillery did -5 damage to cities defenses. Civ 6 modern era cities make Stalingrad look like pushovers by comparison.