This isn't true. Asteroids of this size don't simply break up as they fly through the atmosphere. We've had significantly smaller ones hitting the Earth that made a mess, such as the
Tunguska Event, which was a 100 meter asteroid that caused an explosion of a 5-30 MT yield, which is far,
FAR worse than, say, the bombs dropped on Hiroshima and Nagasaki.
Apophis has a diameter of 325 meters and let's not forget the fact that explosive yield of asteroids grows exponentially with size, meaning that a 325 meter asteroid wouldn't have a 3.25 stronger yield than the 100 meter one. The 100 meter asteroid would have a volume of 53 000 cubic meters while the 325 meter asteroid would have a volume of 1 800 000 cubic meters. That's 339 times the volume, 339 times the kinetic energy upon impact and 339 times the yield. I.e., a yield of 1695-10170 MT.
Just as a comparison, the Tsar Bomba, the strongest bomb ever dropped, had a yield of 50 MT and it destroyed everything in an area with a diameter of 35 kilometers. Apophis would destroy everything in an area with a diameter of 190 kilometers.