Kinshasa's urban area (not the entire province) is generously estimated at 600 square km.

Mexico City is 1485 square km.

Mexico City's population, within that 1485 km^2 envelope, is most commonly given as ~9.5M. (It's ~20M with satellite towns and regions.)

And then consider that most of Kinshasa is comprised of buildings that are very low to the ground -- far lower than in Paris -- whereas Mexico City is in places very dense.