If the iMessage ptotocol is so great (I don't know enough about it to say),
Well, it supports bigger images, read statuses, and fun effects that aren't a part of SMS. But what's important to a lot of people like me is that it's automatically E2EE if all recipients are on iMessage.
I would hope that anybody on HN considers that rather important.
Silicon Valley and engineers in general have really fucking changed if having a large portion of the phone-using population getting automagical E2EE is no longer a big deal.
Until then it's not a standard, open or otherwise.
Are you holding Google to this same standard? RCS is open-ish, but the E2EE extensions are proprietary and the key exchange is managed by Google. They are not opening that up, or at least they have not said that they are.
E2EE is not exactly trivial to make "open" because somebody has got to manage the key exchange. This is true for Signal, etc.... Signal handles the key exchange.
I would have a problem with Apple's conduct here if they locked you out of alternatives.
But I think their approach is correct. You get a default E2EE experience that works between Apple devices. But you are not prevented from any other messaging network you might want to use.
In some ways this is admittedly like Microsoft enforcing their web monopoly by making Internet Explorer the default browser back in the day, but I think it is different in crucial ways and I think E2EE is a worthy and necessary goal.