> owned by the creators of the largest social network in Russia
Another way to describe them is people who lost the largest social network in Russia and are now Russian expats and dissidents.
> Signal, open source [...] With founders that are known to care about organizational transparency and user privacy.
Not open source, only partly, just like Telegram. And founders are known to have a radical position on trading privacy for centralizing as much control over the app as they can, tying identity to phone numbers, etc. They have exactly as much control over the app as Telegram has. But they are not dissidents or expats and who knows what they are going to do or did with covert or overt government backdooring attempts. Still, despite all the flaws both Signal and Telegram are in a bit better situation wrt privacy than Facebook owned Whatsapp, being in a business of compromising privacy and all.