By default Telegram doesn't even do E2EE, you're 100% trusting them not to read your messages unless you start a secret chat. In what objective way could you consider Telegram to be technically more secure than WhatsApp?
Firstly mahnouel didn't write "more secure" but better.
Secondly: if backups are enabled WhatsApp at anyone of the group members then WhatsApp is automatically uploading unencrypted copies of the group chats to Google.
I'd say that brings WhatsApp security for groups down to Telegram level at least.
Thirdly: forcing others to use WhatsApp to be part of the group gives away their group affiliation to Facebook. This might or might not be a problem for you.
Signal's new groups work much more akin to WhatsApp and maybe I can bring it back up again once the pandemic has fully subsided.
I salute everyone here who is able to switch away from WhatsApp. I wish I could dump it as well, but I can't.
Why? I volunteer with a group where one of our main things is to have a small army of people out doing coordinated-but-physically-separated tasks. Everyone has a smartphone of some kind but they're of varying types and quality. We tried using group SMS but that was a disaster, as group-SMS is bad enough but group-SMS-with-30-people is one level below "just fax everybody."
WhatsApp, meanwhile, lets us make daily groups, have a QR code that volunteers can scan at check in to join the day's group, app versions that work on the shittiest Android phone all the way up to the brand newest iPhone. And as a bonus, since almost all of our volunteers have friends and family outside the US, pretty much everybody already has Whatsapp installed and knows how to use it.
The one time our Executive Director tried switching apps, I had to spend an hour talking him out of WeChat, of all things. Point being, we need individual action to pressure our friends and family groups along with regulatory action so that massive platforms can't abuse us like this.