I’m certainly not trying to be an Apple apologist here, as iMessage has plenty to critique. But it bears consideration that iMessage falling back to SMS is a certain amount of openness, is it not?

Not an unfair complaint against Apple, but ignores Google’s/Android’s problematic “support” for RCS, and in this context of this comment seems to imply that What’sApp isn’t “closed” like iMessage.

apple hates open standards

What about WhatsApp is open?