The best evidence for Signal vs Telegram is responses to subpeonas from courts, which has repeatedly shown that Signal has very little info be comparison.
It is the other way around. They already get all necessary info from Signal and Whatsapp directly. If it really was private, the mainstream and govs would be chasing and badmouthing signal like they do with telegram. The NSA museum takes pride on planting exploits that go for decades until being exposed and admitted.