a) Counting areas where resources come from get complicated quick. Are you gonna count the ocean because the grizzly bear eats the salmon? Do Nile crocodiles get their population density counted based on the entire watershed they depend on?

b)There are about 50 people per square kilometer of land. Even adjusted for farmland humans are still gonna blow every other large predator out of the water. Even if you include commercial fisheries that still blows every other large predator out of the water. Maybe there's a couple seasonal localized concentrations of certain predators that are higher but nothing else comes close to that number.

Yeah but it's still clearly way better than wild animals of comparable mass