These things are made up according to the plot requirements and just a loose hierarchy. Such as, Captain America can't just stand still while being shot by pistols or stop a train, like the Hulk or Super-man would, but, if the plot requires, he would be able to knock out the Hulk, even if cheating somewhat, like throwing the shield after a dash in a dramatic slow motion to emphasize effort, or throwing a big safe over his head from the top of a building while he's not looking, whatever. A non-"super" human would have to do something more extreme to achieve the same effect, and wouldn't be able to lift and throw down with force a big safe, for example, instead a more normal human, even with impressive strenght would have to do something like hit Hulk with a full-speed truck with a heavy load or something.
There is no absolute consistency in this sort of thing, be in comics or in movies, they just do the best to keep just a loose consistency while they stretch it quite a bit in order to make some scenes cooler or just "possible". But it won't stand careful scrutiny, it's like on episode A32F7 of itchy and scratchy, when scratchy hit twice the same xylophone piece, but it played two different notes, like only a magic xylophone would do.