You're looking at the features rather than the true value of these apps, the users. Snapchat has the biggest reach into the most impressionable market, teenagers. That's why it is valuable.
That's actually kind of grandparent's point - if your only "innovation" is managing to market to a slightly different set of users, you have no moat, and a big company with some engineer-hours to spend can duplicate what you've done for every market segment you haven't reached yet.
My interactions with teenagers makes me wonder though if Snapchat actually has a reach into that market. Right now their reach is providing a tool that teenagers enjoy, mostly because things disappear and their parents don't see it. As soon as they start to attempt to leverage that reach in anyway that seems obvious, or if that reach infringes on the core experience, I'll bet they're on to the next thing and we're left with something else that was once valuable "because of the users!"
Snapchat is valuable from a monetary perspective, but actual real value is little to none. No one is going in 10 years will say Snapchat changed our lives or progressed society's knowledge. People will look back wondering why it made a handful people beyond wealthy.
Considering AIM just got shut down, that's a rather poor long term outlook.
Which I think is the point. To be a new billion dollar company (vs pump and dump) you need to either make 100's of millions in profit for a few short, but profitable years. Or, have steady profits and steady growth over a very long time scale.
You're not wrong, but the 'frightful 5' were all transformative for society. The point is that the big companies quash non-transformative small companies.
Teenagers grow up, and the next crop of teenagers would use not Snapchat but QuickBlah or FastYap or something else. There is no inherent advantage to Snapchat, it's just luck that they happened to be the one there. It's like finding a suitcase with money on the street - valuable, but not sustainable.
The same teenagers also don't have much spending power now. And besides, teen trends change pretty quickly, so their main targets are teens it does not bode well.
That is the key transition. Once they start greying, users will perceive any new platform as unwelcome change. But until then, you have to eventually give them better reasons for staying than just "this is younger and wilder than that other thing".
Facebook's ticket for growing up in lockstep with their core user generation was coordination and communication for loosely coupled groups with some real life connection. People who move into a new development, the "parent cohort" around a daycare class, new hires who joined a company at roughly the same time and so on. All that is young adult stuff that fits well with what Facebook offers.
Nonpermanent asynchronous video messaging? If interpersonal exchange is always a blend between information propagation and entertainment, Snapchat seems dangerously lopsided towards entertainment. That is good for getting people excited (quick growth), but probably not so good for long term retention. MySpace was similar.