They are trying to show Apple is intentionally doing vendor lock-in. Apple argument that software across different platform is competing with each other gets weaker as vendor lock-in increases.
iMessage isn’t vendor lock-in. If you’re on an Android, you can still send me an SMS or MMS to my iPhone running iMessage.
The iMessage experience is vastly superior to the SMS & MMS experience, but that’s hardly anticompetitive. A BMW drives better than a Kia too. That’s not “lock-in,” it’s just a better product.
Google had a shot with its efforts around RCS, but as with most Google consumer software, it was unreliable, slow and of poor quality. Carriers recently dumped it.
The answer isn’t for Apple to be forced to give up its stuff to the competition, the answer is for the competition to not suck. Android controls 90% of the mobile market, and if Google created a non-crap messaging standard, Apple would have to end up supporting it.
The other problem is that the thesis that a messaging platform protects an ecosystem was already disproven with BlackBerry Messenger. It was once dominant, and BB didn’t release it for other platforms until the BlackBerry was in severe decline. People happily ditched BB for iOS and other platforms even before their was an iMessage.