Well, now about a half of decade passed since that expert opinions were raised. And no data-breaching bugs were found in Telegram, but there were plenty of them in WhatApp.
Surely, that doesn't mean that expert were wrong, but at least mentioning that in Telegram vs WhatsApp debate doesn't look like a strong point.
Its funny and sad that telegram developers at the same time dismiss their own past history of security vulnerabilities with "all programs have bugs", but then they attack an app with superior encryption protocol by complaining about those same bugs that get patched when they are found. Pathetic.
And like heinrich5991 said, there's no need for backdoor or vulnerability when the data leaks by design to the server.
And no secret chats aren't an option. E2EE needs to be cross-platform and enabled by default. Signal can do it, Wire can do it. Telegram can't, because the developers are completely incompetent.
Surely, that doesn't mean that expert were wrong, but at least mentioning that in Telegram vs WhatsApp debate doesn't look like a strong point.