The fact that WhatsApp is non-free and backdoored <https://news.ycombinator.com/item?id=13389935> is a good enough reason not to use it instead of telegram (or wire or signal or tox or most e2e programs).
Well, if "snakeanus" on Hacker News says so, why would I believe Matthew D. Green, Bruce Schneier, Avi Rubin, Steve Bellovin, Emin Gün Sirer, and Paulo Barreto when they cosign a letter saying that report was horseshit? Tough call, I guess!