Like I said, the chats are stored (or are claimed to be stored) in an encrypted form. But I think I understand why it may count as "stored unencrypted" in your eyes. Still, Signal won't cut it. It's too inconvenient to use, and while maybe it provides better security it's like a very strong password policy in a company that entices users to just write down passwords on Post-it notes.
I couldn't get my friends use Signal, it's not there yet in terms of user friendliness (hell, I wouldn't use it). But Telegram works for me, and I consider it a substantial improvement over Whatsapp. YMMV.