Well I don't read much Bronze Age comics, but I see it a lot in more contemporary comics. And I see creators writing their character "their way" in pretty much the majority of the comics I read. If their way doesn't include the main character being an engaging misanthrope doesn't mean they didn't have the guts to do that. It just means their vision was different.
Dave Sim was of the generation that started reading comic books just as the idea of the "comic book artist as idol" had just taken hold on the fannish subconscious. Stan Lee's celebrations of his fellow pros mostly got the ball rolling (in contrast to earlier such experiments, like EC, where the idol-ization had less cumulative effect). A handful of DC creators approached comics with the idea that they ought to be allowed to do, say, Batman "their way," with Neal Adams standing as one of the earliest such examples. Sim has written of being strongly influenced by Adams in his youth, though there were also a lot of Bronze Age creators-- Steve Gerber in particular-- who also promulgated a reputation for highly individualistic takes on their characters. Sim was well positioned to take inspiration from such figures.
Of course it should be said that merely being exposed to individualistic talents doesn't make one inclined or capable of delivering individualistic works.