The point is absolutely not « is Signal secure enough to conduct government business including decisions to use lethal weapons to kill people? » (it is, if you’re not stupid enough to invite journalists there. Or let me talk to you about Macron’s entourage being big Telegram fans, as a treat 🥸).
The point is using a not archivable channel, which is strictly forbidden under US federal law to conduct gov biz. Not that anyone cares at this point.