I would like to agree with you, but the difference here is that the IPhone can do much more than the watch, and in many cases better, so the $600 was justified. The watch on the other hand still requires the IPhone for many of its features to work. If it's not compelling enough, the price should go down. I for one would jump on it right away if the watch is independent or standalone. As for now, I am still thinking about it, and I can't wait to try one on to fully decide.
That and the iphone at first didn't sell that well. It was reduced though it was through subs. And even more later to 199.
Fast forward to ipad. It sold well for not being able to do much either. It was basically a big ipod touch.
I would still argue the watch is like the ipad. Neither is needed. Given how much ipads have collected dust for me in the past, the watch may end up being the better buy. You can't help but use it if it's on your wrist.
I talked about this in comments but the watch will be your most used device. It will be your first line of notifications and info. That's what you have to consider in value and money spent. If you only use your ipad a couple hours a week, then how much value is that compared to a 12 hour a day, always on and nudging you, apple watch?
I wouldn't worry about what device can do more.