That’s not the issue is it though. The issue is the metadata around SMSes which Signal does not have. You still need this Deku app on both phones, and if you’re going to that effort, you might as well use something that solves the problem.
Not E2EE, whereas RCS+Google Messages is. I wouldn’t be trading a promise for a technical requirement that messages can’t be read. Google cannot read E2EE messages even if they wanted to.