I was ready to say "not necessarily" when I saw the title. But as I read, I changed my mind on some aspects. If Sony hadn't stepped in with the PlayStation and kept doing 3rd party consoles for Nintendo, industry would've been different from what it is today.
I agree on most of your points, but I wonder who would've explored the adult demographic. Could be Sega. But would they blame the failure of their products to that demographic they failed to sell to?