> Telegram vs Whatsapp in terms of security.

The 3-letter US agencies do not have direct access to Telegram's servers, they do have when it comes to Whatsapp (or to any other US-based company). The same goes if you're a Russian doing anti-government stuff in, well, Russia, it's better to put your fate in Whatsapp's (and Meta's) hands, presumably the US agencies won't come after you for being against the Russian government. It's a classical game of arbitration (for lack of a better word).