The jaguar (onça-pintada) should be higher. They are arguably the most powerful predators of the Americas. They can run up to 80 Km/h; they can climb trees; they have jaws strong enough to crush bones; they are proficient swimmers, being able to hunt prey in the water, including alligators; their roar is bone-shivering; they are stunning and iconic; they are important for the ecosystem balance. Note that while the jaguar may be phisically similar to the African leopard, the jaguar is faster and stronger, and a better swimmer.
Last I checked Grizzlies and other bears live in American continent so that rules out the most powerful. Yes all other big cats do the same thing, and they don't hunt alligators but caimans, alligators are too big. It's basically just a black version of other big cats.
The animal I talked about is called "onça-pintada". It's not necessarily black. It's the third biggest feline, being smaller than the tiger and the lion. It's the most powerful predator in Amazon rainforest. People often say it's the most powerful in the Americas, but they are wrong, then. I didn't know the english words for "onça-pintada" and "jacaré" and just put them in translator.