While it's true that Amazing-Man and Stars & Stripes ending up with fairly different line-ups, in many cases, these features were created by the same artists, making it difficult to understand how putting out two roughly bimonthly titles with most of the same creators, some doing the same characters and some not, was a better business move than putting out one monthly. I doubt any deadlines were saved by running Electric Ray in place of Mighty Man. And if Centaur's distribution was as spotty as I've heard, it must have been aggravating for their readers when continued stories like Mighty Man's battle with the Witch had chapters that ran from one title back to the other, assuming that kids cared about stuff like that back then.
It still seems to me that filling a title like Stars & Stripes with the lead features of their other titles would have made more financial sense than cloning another title and then running a bunch of random tryout features thru both. As much as I enjoy Mighty Man & the Shark, I have to assume that Masked Marvel and the Arrow had to have been better draws, since they did get their own titles, while the Shark only made two cover appearances (and one of those was just a giant version of his hand!), and Mighty Man only one. Admittedly, that one was on Stars & Stripes #2, the first issue of that series, and as near as I can tell, the only "group shot cover" in the Centaur line (Fantoman & Speed Centaur shared a couple sort of split covers, but this was the only "All-Star" type cover I'm aware of here).
Of course, Centaur was rife with odd editorial choices, like sending Zona off to become a super-hero one issue, only to put her never before seen kid brother in that role in the next, and no mention ever made of why Zona's stay in Tibet never seemed to actually happen (most of the features in AMC had tighter continuity than much of what's being published now), or creating a rewritten and redrawn origin for Dash Dartwell for The Arrow #3 instead of merely reprinting the old one, given that Centaur was clearly not shy about running reprints.
At this point, I guess we'll never know what they were really thinking...
-Comicsnorth