It looks like that is how they’re currently implementing it, they are sending to the providers as well but this is how they’re doing it with the app itself currently. So you are correct if you’re using anything that isn’t Google messages currently it doesn’t do anything

I’m expecting this technology to eventually evolve to have a setting where it detects if the person you’re sending to is currently on a technology that supports it and will warn you, like how the RCS system currently Works