some quotes from an article:
However, as much as Weisinger might have tended to domineer during his peak, he found that other forces in DC could move him as well. Consider the case of the creation of the Justice League at the dawn of the sixties. Bob Kane and Mort Weisinger, respectively, thought that including DC's most recognizable creations, Superman and Batman, might overexpose the characters. Both sought to keep the heroes off the covers of Justice League of America, and, if possible, out of the book altogether. Had these men had their way, a Justice League very similar to that of Waid's JLA: Year One might have appeared in print originally, not just in revision.
Weisinger, according to Schwartz, wanted Superman left out of the Justice League of America (except, perhaps, in the occasional end-of-story one-panel appearance), possibly owing to fears of overexposure of the character and possible market saturation.
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http://www.fortunecity.com/tatooine/niven/142/talentpo/tp23.html