Due to regulations I think it is difficult to find any fintech which a small bootstrapped startup in the traditional sense. Some bank tie-in is needed. And by that I might be overloading the startup moniker.
My point was that they're still tiny compared to the giants such as AmEx or Visa. And it shows that the old players can be unseated faster than expected.
It has been amazing to see how fast such apps gain penetration in the market.