Making your own products interoperate better than competitors' products is pretty typical and I don't think it rises to the level of "anticompetitive practice."
If you don't like it (and I can totally understand why), there are numerous other smartphone makers out there with products that allow better integration with these watches and you're free to buy one.
MS didn't get into trouble because they went after competing browsers, they got into trouble for doing that while also having a monopoly on PC OSes. Apple doesn't have anything like a monopoly in this market (their US market share is about 50%, worldwide is around 28%).
Microsoft absolutely got in trouble for purposefully making other Office suites not work correctly on Windows, for using private Windows APIs in Office that other companies didn't have access to, etc.
If Apple makes a watch that can receive and send iMessages then there is no reason any other device shouldn't be able to use the same APIs that Apple uses.
It absolutely creates a system where competitors literally cannot compete with the same features.
They got in trouble for doing that stuff while having a monopoly on PC OSes. Using private stuff to give your own products an advantage is (legally) fine if you're not leveraging a monopoly to do it.
If you don't like it (and I can totally understand why), there are numerous other smartphone makers out there with products that allow better integration with these watches and you're free to buy one.
MS didn't get into trouble because they went after competing browsers, they got into trouble for doing that while also having a monopoly on PC OSes. Apple doesn't have anything like a monopoly in this market (their US market share is about 50%, worldwide is around 28%).