WhatsApp/Signal and Telegram are completely different platforms. The formers focus on end-to-end encrypted conversations, while Telegram focuses on speed, functionality, and security. While I appreciate their open-source client apps and promise for offering a secure chat experience, it doesn't change that their chats (1:1 non-secret chats and group chats) are not end-to-end encrypted. WhatsApp and Signal are superior solutions in comparison.

Edit to add: My point being, with their focuses (at least Signal's) being on offering end-to-end encrypted communication, it feels normal that they are not able to focus efforts on improving client experience. Hopefully something that they are able to achieve in the coming months.