I think you missed my point, which is that WhatsApp is already rogue by way of metadata collection (which is as valuable as content), and that there’s no way anyone can claim with certainty that it’s not gobbling up more data on the server. Even Signal has stopped publishing its server source code for nearly a year, and if we are playing the game of what Telegram is doing with the data, we can say the same about Signal too on metadata (now that more information about groups and group memberships is stored on the servers).

We don't need to play any games to point out that Telegram can see everything, including messages.