This.Actually, Superman being the 'first' hero in-universe has never really been as much of a thing as people seem to think it was.
Back in the Pre Crisis era, most of the heroes' books pretty much existed in their own little universes, barring the team books. So the notion of Superman (or even Superboy for that matter) being the 'first' was never really brought up, to my knowledge.
The only mention I recall of Superman being the 'first' was this one panel with the Earth Two Superman, and the narration saying that he was the first hero on any earth...a tip off the hat to someone meant to be the 'original' version of Superman of course, but one that doesn't really stand any scrutiny (given that we are dealing with infinite earths!)
Post-COIE, Superman was established as being the 'first' of the modern era of heroes, once DC started getting serious about things like timelines. And in the New 52 too I think he was supposed to be the 'first'. But to my knowledge, not a lot was ever done with this. There were no significant stories, or even scenes, that really delved into the implications of Superman being the 'first'. I can only recall Manchester Black referring to Superman as "the first. the best" but nothing other than that. Of course, I might have missed something.
Also, logically speaking, Superman did not directly inspire any of the other characters to become superheroes. Bruce was training to be a vigilante long before Superman showed up on the scene, and his decision to become Batman was based on the bat crashing through his window. Barry became the Flash because he was inspired by Jay Garrick (I don't know how that stands currently...haven't read Flash Year One yet). Hal being chosen by Abin Sur to be a Green Lantern had nothing to do with Superman, nor did Diana coming to Man's World, or Arthur Curry deciding to use his powers to patrol the seas.
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