I don't get why you would give up on E2E when you can just switch to Signal, unless you use Telegram for some features that Signal does not have (I don't know if there is any TBH), but you do not list them in your three points.
It would also make sense if more people are already on Telegram (so that you have less people to convince to switch), but again you don't mention this reason to prefer Telegram over Signal.
In my case, as usually advocated by security expert, I prefer Signal, and I fallback to WhatsApp whenever it is too big a hurdle to make people switch.
Or better, switch to Matrix. Also E2E but without the lack of features (like multiple devices and a desktop app without a phone proxy) and odd obsession with phone numbers that Signal has.
Seems I am getting off the hook easily with my campaign against Whatsapp then.
I'm at a double digit upvotes and that is even when I have seen a few downvotes in a row : )
My biggest gripe with this has been how some of our cryptography stars IMO has a very one-dimensional view on this:
"E2E good, anything else bad."
IMO, E2E message encryption only buys you so much, i.e. as a thought experiment one could consider if you would like to use an E2E protected system run by NSA. Or by FSB. Or by our bosses, wives, parents etc. Whoever you don't want to make statistics on who you contact and when.
For me who like to think I am smart to keep as much data as possible out of the hands of FB - and by that - out of the hands of
- whoever buys the windfall when Facebook collapses or
- whoever manages to hack them thoroughly or
- whoever sends them a valid subpoena or
- (slighly evil here) pays them enough
OK, Facebook guys - let me cut you a deal: you start acting trustworthy and I start liking you. I want to like Whatsapp. I want to pay you money. I want to pay you more for API access. I want to have a brilliant messaging platform to communicate with my stubborn family.
I just don't want you to ruin product I loved. I don't want you scheme so hard to datamine me that you need to update the privacy policy.
It would also make sense if more people are already on Telegram (so that you have less people to convince to switch), but again you don't mention this reason to prefer Telegram over Signal.
In my case, as usually advocated by security expert, I prefer Signal, and I fallback to WhatsApp whenever it is too big a hurdle to make people switch.