That reminds me of Punisher movie, where the Punisher was caught and interrogated by bad guys, and he said he was sent by Batman. So the people of Marvel Universe at least heard of DC comics.
Batman also was a spy during Silver Age, when WWII was a common topic of the comics.
This power imbalance they're discussing, I've seen it handled in different ways.
The simplest to explain - but it only works with the willing - is characters are at different power levels. For a game like D&D, it'd be different Levels. For a game like GURPS, it means radically different total Character Point values. Either way, it is the narrative that explains how they all come together as a group. Either the circumstances mean they're more or less equally valuable or there are enough things for the non-heavies to do that no one feels left out or gets bored. This can also happen naturally in some games, where new players don't start out more or less on even footing with established characters, but must begin from a lower level/lesser CP total/etc.
The other way I can better explain using GURPS, but it might actually be easier in something like D&D. From what I know and have experienced with D&D, it has built-in niche protection. So the combination of a PC's race, Alignment, and/or Class can prevent them from doing various things, or doing them as well or cost-effectively as a different combination of race/Alignment/Class. With GURPS, it is easy to underestimate the value of "mundane" traits. In GURPS, a character's total CP value can give you an idea of their "power level". Besides how well they're built and run (a factor with most RPGs), someone worth 1000 CP would be an experienced or powerful superhero, god (of the Roman-Greco variety), etc. There are at least a handful of humans alive right now who are probably 1000+ CP characters, and hundreds who are in the mid-to-high... hundreds. How do they reach such levels while still being competently built? Social power. We're talking about the heads of powerful nations or corporations who also have decent-to-high Attributes and/or Skills. There are also highly trained, conditioned soldiers who flip the two around; high to peak human Attributes, and a good deal of social power thanks to their Rank, military organization's reach, etc.
Batman combines both and then some. Typical attempts at rendering Batman in GURPS will see him with near peak Attributes (worth several hundred CP), massive amounts of wealth and advanced technology at his disposal, a wide variety of Skills, and many of those Skills at extremely high levels. Then, for good measure, add some "narrative" powers, like Luck, Serendipity, Extra Lives, etc. that could be used for more supernatural things, but for Batman? They're explained (and sometimes Limited) to representing how Batman is just that good. The fact that he's not going to be affected (or affected as much) by anti-super, anti-magic, anti-psi, anti-tech, etc. measures is also important.
Getting to Hawkeye and Black Widow, neither is Batman, but they are in the same vein. Like some versions of Batman, they also have access to "gadgets" that are basically super powers in their own right. Just not as blatant as Tony Stark with his Iron Man suit. ;)
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