Ask HN: How do banking fintechs like Revolut justify their bn-$$$ valuations?

Hey,

we are evaluating banking fintech ideas (=startups, which deal with banking services, examples: Revolut, N26, Brex, Scalable Capital) and every time we calculate market sizes or potential profits, we come up with very low numbers, which never lead to the unicorn valuations that those other Fintechs claim.

What are we missing? On which story do they receive their massive fundings and valuations? Should we do a banking fintech?

Example: Current Revolut revenues per year: ~30m EUR; if they 10 fold their revenues, and start to generate a 20% profit margin (instead of loosing money on every customers as they currently do), then we have 300m EUR revenues x 20% profits = 60m EUR profits / year = 900m EUR valuation, considering a multiple of 15.