Telegram hires excellent developers and was started by someone that had successfully run a company before. The clients for the different platforms in the case of telegram were developed by very small teams (1-2) of exceptional programmers.

- macOS client: https://github.com/overtake/TelegramSwift/graphs/contributor.... Written almost single handedly by one developer.

- Telegram Desktop: https://github.com/telegramdesktop/tdesktop/graphs/contribut.... Written almost single handedly by one developer, who also wrote almost all of the supporting Qt code.