I do not like this decision. Using Signal as a main SMS provider makes it easier for me to collect all of my messages in one place. Now I have to, YET AGAIN, download an SMS app for use while keeping Signal active. I'm glad privacy is becoming mainstream but dislike lowering the bar for adoption to where it profoundly affects users.
That's what is nice about signals implementation is it stands. It supports acting as the SMS default app on android and defaults to signal when it can.