You're saying that a company can't be sustainable if its spending exceeds revenue, but there are plenty of institutions that do exactly that and are based on th

You're saying that a company can't be sustainable if its spending exceeds revenue, but there are plenty of institutions that do exactly that and are based on the same premise as what we know about Telegram's funding. A single (or multiple) large donor(s) can potentially donate enough money to make a thing sustainable without relying on much if any revenue. There are examples of that in the real world.