Also, Whitebeard's destructive power and his ability to withstand damage done to his human body are two completely different things. Had he used his power to its full extent, he could have potentially wiped out all human life from the planet due to plate tectonics, but he likely couldn't have devastated huge armored beasts of Toriko-verse. And he definitely couldn't have taken a single hit from them because his body was still that of an ordinary, albeit incredibly strong, human.
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Well, if the Human World population is over 30 billion and is just a small part in the center of the world, you can make yourself an idea.
The population could be really tightly packed, though. Its size alone doesn't mean anything. But for there not to be huge wars over diminishing resources and food shortages? Yeah, pretty darn big.