[rafiki6]

It always comes down to "can you do something better than they can?". For all intents and purposes, the oligopoly is doing ok, is not egregiously expensive for the service they offer, and has first market mover advantage. They are innovating and providing value. There's a real barrier to entry like you mentioned in developing the required relationships with financial institutions to have enough uptake in most of the developed world. Non visa/mc alternative payment networks tend to take off where there aren't already established FIs or where they are very anti-western influence like China.

Best bet here is to target some aspect of the payment lifecycle that one of the incumbents isn't focusing on. That being said, if successful you're more likely to just get acquired than to topple the dominance.

Frankly I don't think it's worth it to try to disrupt this industry. It seems that some player always comes through to help modernize to some degree. Payments are a really boring, yet surprisingly complex space that someone else has already solved (from a consumer perspective).

There are many other aspects of the financial system that might be worth targeting.