It was not an assumption, it was my opinion.
I've never built a "disruptor" bank but if I were to do it, I wouldn't hire all my staff from a traditional bank. It's like expecting a 747 pilot to re-train as a fighter pilot. Sure, they know a lot about flying airplanes and they could probably do it, but it doesn't necessarily make them the best fit for the role.
What I can tell you from experience is that it's very difficult taking bank staff in their 30s, 40s and 50s, who have worked on mainframes at the bank since their early 20s, and teach them about virtualization, containerization, microservices, agile, dev-ops, etc.