I don't understand why the sms thing is such a big deal. Either use it or don't, as in, I use shitty sms android when I must buy the majority of my communications are done through signal. Sms is not secure and should be avoided.
Op regarding your edit, your title says privacy open source and security , it says nothing about for piracy. I'm aware we're on a piracy community, but that's not what your title said.
Signal is the best, honestly the tech is unbeatable. If you don't want to use a phone number, then Session is similar albeit with less robust encryption protocols.
I mean yes but not really comparable to what's supposed to be a pick up truck. It's no different than saying your Prius is more efficient than an F150 lol
Do FOSS apps like Squawker rely on the same api I wonder