None of the adjectives nor concepts you have applied to SMS apply, including the assertion that any number of clients can interconnect peacefully, that it is open, that it is a standard, that the steering of the technology is not actually done by the private surveillance companies you’ve mysteriously overlooked, not to mention how SMS is easier for law enforcement to acquire than a pack of cigarettes, because the carrier is sitting there waiting for a warrant on account of not angering the government that, you know, gave them spectrum and allowed them to exist in the first place.

Aside from all of that, good analysis.

Aware iPhone owners literally have the “oh, they’re green, looks like I have yet another plaintext compromise in my life and they’ll never figure out Signal” conversation with themselves every time they exchange numbers with someone new, and I’ve met more than one person who has remarked negatively to the person’s face that they are using SMS, including in a dating scenario as a dealbreaker. You might be the only person who likes it, aside from misguided parts of the Android community that praise SMS roughly like you do when discussing the lack of something like iMessage in that ecosystem, all without realizing the surveillance calculus you’ve correctly established is the real reason the carriers tie Google’s hands (even beyond Google going through messaging systems like socks).