Earlier quoted context omitted.
Having just installed Signal yesterday, in what respect is it worse than Whatsapp (from a UI pov)? The only thing I found so far is the bad integration with contacts.
Having used Signal, Telegram, and Whatsapp heavily (friends on all three, natch), here's my one absolutely critical beef with Signal: It doesn't always deliver messages, and it more frequently doesn't deliver them in a timely fashion. In my experience, Signal delays delivery of messages about 5% of the time -- which is actually huge and makes it unusable for reliable chats. The story which made me never trust Signal…
I agree with the SMS replacement for Android and uninstalling causing woes trying to send secure messages, have been bitten by that one on several occasions. Thankfully most people I talk to have multiple apps installed.