Ideally then you’d limit the amount of SMS messages you send at all, and use a secure messenger like Riot.im.
There is no such thing as 100% security and privacy but we should strive to achieve the best security and privacy that we can.
One random app (Facebook in this example) can NOT access another random app's (sms in this case) data on an iPhone where it can (or could before the very current version) on Android.
YMMV: You might call that "Freedom" and "not a walled garden", I call that cross access to data a nightmare and am happy that it is a none issue on IOS.
But it can. You're just wrong here. The Facebook app running on other nodes in the network does have access to at least part of the data you are suggesting is totally private. That data is duplicated and not only on the phone you have 'control' over. That data is not private. Facebook can and does still get it.
Also, Facebook is not some 'random app', and you know it.
Facebook even has a history of having its own code embedded inside of iOS itself. This is not trusted and not safe and clearly not 'random'. Apple does not randomly include code from other 'random' apps into the core of iOS.
How is that a non issue? Just because one permission on iPhone prevents Facebook from sucking up that particular data point right now hardly makes it a non-issue.
Surely someone in your family is texting an Android user any way. And Facebook is not upset by the lack of info your family is sending them, I'm sure.
Dismissing major privacy concerns as non-issue just because you have an iPhone seems super dangerous to me.