I can see some benefit with Signal being open source.
I think this may have been resolved now. However the issue remains that you cannot delete signal contacts and legacy groups, which means anyone who gets a hold on your phone number (without a pin) or phone, or account access to third party involved, got evidence for communication between you and a possible incriminating entity.
> Contacts must be blocked in order to be removed from your Signal Contact List. To learn how to block someone, click here.
https://support.signal.org/hc/en-us/articles/360007319011-Ma...
You either have the contact in your contact list, or block list... I hope that's obviously supporting my claim.
Some of these meta data leaks may have been changed and are a result of my old account, however Signal lost my trust. (And lost sympathy over Moxy Marlinspike's opinions and presentation over time, e.g. the hangover/drunk "centralization: good" CCC talk, the F-droid drama, ...)
Whatever flaws Telegram got, it seems less impactful than getting mined by facebook and the practical design failings of Signal.