Well for me the experience is the important thing, not the device. I don't really care how it's done as long as it is done in the best way possible. I will change the device as soon as there's a better experience somewhere else. I'm sorry to say that I have almost no brand loyalty, perhaps with the exception of cars.You're not really comparing similar things in this way. You're expecting the Apple Watch to be able to natively stop/start/save to a device that it didn't make. Can't expect that. If Polar makes the Polar watch app in such a way that it can stop/start/save data from the H10, sure I can see that.
The best experience possible means minimal fuss and maximum output. Once people start with "but you can subscribe to app X and it does the same thing" or "but you can import the data from X to Y" I just lose interest. That's not a good experience for me. I don't want to spend my time doing that.
It's very important to get one good health/fitness app, not several, get everything in there with minimum tracking effort, get as much data and interpretation out of it. That's it. Otherwise I don't bother, it's not worth it.
To give you another example: I like to do sleep tracking especially as it integrates into the training readiness situation. I could not do sleep tracking with an Apple Watch. If I have to take it off in the evening to charge it, you can bet your house that I will fall asleep with the watch in the charger and remember it the next morning. It's a non-feature as far as I'm concerned.