I appreciate the response! Re platforms like Parse — it is ironic you refer to it as a startup given that it is Facebook which is shutting it down. I think of parse though more as a service layer since it doesn’t give any distribution advantages — so is a little different consideration and risk set to depend on.
Re your point about other products getting big alone- that isn’t quite true. As Facebook started growing beyond college, it depended on growing virally through hotmail, yahoo mail, gmail, and AOL instant messenger. One can argue that “email” was a more open platform — but all of those companies had strategic advantages with their contact lists and ease of sending email and they allowed FB to scrape them. Others have now used mobile contacts and SMS invites in a similar fashion. Instagram grew leveraging FB and Twitter, Pinterest leveraged Facebook heavily, and there are many more.