i'd say Vomics are more an indicator of how well a series has done rather than something that causes it to do well. Still, exciting for voice actor nerds.
Also to pipe in on the older train of thought the existence of a "big three" is a laughable matter based on titles that were making an impact internationally (something that Shueisha themselves are unlikely to notice, considering how atrocious western manga sales can be. Sure, three or so titles tend to be put at the front of group shots, but that's naught but the result of market research. those are the faces kids are more likely to know and to want to read the stories of. Marketing is clever like that.