That's not entirely true. Telegram's one on one secret chat is end to end encrypted. As well as one on one voice and video calls. Group chats are not end to end encrypted.
Additionally Telegram does have an auto delete features built in for all of its chat types. So while I can't entirely rule out that Telegram could have a backup of a chat somewhere, you have a bit more piece of mind if you turn on the auto delete feature.
Why businesses continue to trust Microsoft I'll never quite understand. The number of breaches Microsoft has had overall the last 5 years is amazing. Compare that to what I believe is the ZERO breaches Google has had in the same time frame. Not that Google is to be trusted, but if anything of magnitude would have happened there it would have certainly leaked by now.
Cloud at this point is very hard to ignore. Internal IT team sizes shrinking, it's becoming harder running all of those business needs internally. Businesses will learn the hard way when they continue to put their trust in the cloud, especially Microsoft's. Some facets of IT are just too much work to bother with keep hosting internally. Exchange is a steaming pile of garbage. I managed it for years, so I can see why people cloud their email. Which I'm all for, because email is just a bitch to run in general. But use Gmail or something else. It's a night and day difference. I'm dreading the day my company decides that Microsoft is the better deal just because Office needs updating. Instead of keeping the status quo, spend the money training employees on alternatives and run as far as you can from Microsoft's hold.
Microsoft makes a lot of good products but keeping them secure is an after thought.