Tanks can cause a lot of damage. But one tank isn't going to kill over 700 people with one man operating it, and a questionable amount of ammunition. Even Pierce Bronsan
Couldn't pull that one off.
1. Demolish some high-rise building with the tank, firing HE rounds into the ground floors, hitting the pillars supporting the building.
2. Drive over cars on some cramped expressway, firing the machine guns while doing that.
3. Drive into a nearby rail station, bus station, airport and/or harbor, hitting passenger passenger trains, buses, planes or ships.
All these scenarios can kill hundreds of people, if the attack is carried out without warning and evacuation has not taken place yet.
It's all ASB of course, since noone would ever get the chance to still a fully armed tank, but I am just saying, that a fully armed and manned tank can cause mayhem in a dense populated city.