Most here would agree that a public API is a liability regardless. Anything you can keep private (SPI) you should.
Opening up an API that has all manner of hooks into your Apple device is going to be (obviously, I think) one of the most challenging of API to expose. While a 3rd party watch might needs these API, a whole lot of n'r-do-wells (looking at you, Meta) will likely figure out a way to exploit it in their apps.
It's a can of worms or a Pandora's Box if you will. If Apple is forced to expose these API, but only after kicking and screaming, I would not be surprised.