As I see it, the key advantage of Telegram is not technical, it is political.
Yes, Telegram is a slightly shady company with an ambiguous business model and a possibly-dodgy encryption algorithm (when it is even turned on).
But Telegram is based outside the reach of the West (in UAE, eastern Europe, maybe even Russia). Whatever its other problems, nobody thinks that Telegram is under the thumb of Western governments, as the Big Tech corporate messengers almost certainly are.
Personally I don’t care much if Russia or even China is spying on me. Because if we can be certain of anything in this world, it’s that Russia and China are not sharing their spyware data with Western intelligence agencies. And as Westerners we live outside the reach of the Russian and Chinese police states, fortunately. So for us it’s win-win for privacy. That’s the way I see it.
The ideal solution, of course, is a truly private messenger which protects everyone’s privacy, including Chinese and Russians.