Lots of people here in Germany use Telegram for their purchases of substances (a serious crime here) because they consider it safe. If there's a danger of Telegram sharing their data with the police, the app is no longer safe. If it it's no longer safe for one thing, people won't use it for anything.
Purchases are where the sales at. Strange that these sellers aren’t using more secure messengers.
I believe that illegal activity is a good litmus test for a messenger, much better than forum theories or headlines. If for some reason drug dealers stay away from particular apps, so should you.