According to Sturgeon's law, 90% of everything is crap. But...
How did Facebook come about? Mark stole it.
Had
Evan Spiegel et al been careless with their idea of a messaging app that disappears messages, someone was going to "steal" it.
MySpace was pretty similar to FB, wasn't it? It was also first by quite a long time.
I'm very well aware that I don't really know how to make an app successful. What I do know, is that it's not necessarily being first. It's not having the most features. It's not really even about being better.
It's adoption. People use the app other people use. Many years ago, colleagues of mine worked to make some kind of app that would help you get comparison prices to your phone, or can see specials in a mall or something, I forget the details. They were in talks with some companies, they had their app released and it was available on the app store.
And a few months later when I saw something like that... it wasn't their app. They were first by a long shot, they just didn't have the users.
Obviously it didn't work out for anyone, but even compared to their competitors, they lost even though they were first.
In my experience, first impressions also count. If I try something now and it seems cool, but is too much of a pain, or is buggy, or for whatever reason, I probably won't look at it again until I see that it's really popular.
TL;DR: being first isn't everything. Get customers/users, and make sure whatever you put out is high quality by the time your customers use it.