Perhaps my analogy was bad, but my point is that MySpace and Facebook were extremely similar services which made Facebook a direct competitor.
When I was younger people would use MySpace to stay in touch with friends online, then for various reasons Facebook grew in popularity and people used Facebook to do basically exactly the same thing they were before on MySpace.
I don't think this is the case for Instagram and Snapchat. It's like comparing Facebook and Twitter. Twitter is where you go to share random thoughts more or less publicly to friends and followers. Alternatively, Facebook is where you go to share much more intimate content with close friends and family. And LinkedIn has a different purpose again.
One might dominate in many ways, but there is a reason why I have a public Twitter and LinkedIn and not a public Facebook. There is a reason why I post random photos and songs I like to Twitter and not to LinkedIn.