And looking at their documentation isn't proof.
A sniff of the network while the device is on can sometimes point out 'unexpected' communications with unknown devices. If it's a different platform.
I'll wait for the guys that love doing that to see if spying is going on.
/johnny
Johnny. The iPhone has been tested every which way for that kind of spying in just the way you suggest and it has not been found. The Apple Watch has to go through the iPhone. QED. Apple has not been found spying on anybody to date, why should they start now? The Watch has no camera. So, no spying by camera. It does have a microphone. . . but it has to work through the iPhone. The iPhones have been tested for what you are looking for over years and been given a clean bill of health. Ergo, no spying.
You can be as pessimistic as you want. . . but every time some one has claimed to have found "spying" by Apple it has turned out to not be what they thought at all. Apple has made it impossible for even Apple to break into your iOS devices and get your data or into your iCloud accounts because it is encrypted to 256 AES standards and only YOU have the keys. Apple does not and cannot get them. If the government demands access, Apple cannot give it to them. . . because, again, they do not have the keys. YOU do.
For anyone to decrypt your data without your key if you use just a 16 character passcode, which is turned into a HASH, which then gets entangled with the device's UUID, would require trying every one of the 220140 possible key combinations. To do that would take 492 undecillion years. That's 49.2 times 1035 years. Since the half life of a proton is quite a bit less than that, the Universe would have long since returned to the primordial soup of quarks and other basic particles before they finished trying to find your key. . . and I think it might be moot by then.