Do you have an Apple Watch? Is this review based on your experiences using it for some time?
I think in practice some of your guesses about notifications and interruption are proving wrong for most people because of the phenomenology of the Taptic engine.
I haven't used it but I think there are some biases going in that would affect how I feel of it regardless. For example, for my iPhone, I limit notifications to calls and SMS. Except for the occasional marketer, phone calls are normally "important", and I'm not sure, Watch or not, how I could effectively whitelist calls in such a way that would not block the myriad of important calls from first-time numbers.
In terms of text messages: I guess it's hard to think of a situation in which the ability to glance at my wrist instead of investigating the vibration in my pocket is a huge advantage. Text messages can sometimes be important, but if I'm expecting a text message in a given time period, I'll put myself in a situation in which having the phone out is not a problem (i.e. not be in a movie theater).
I guess one situation in which having a watch is better than a phone: when you're moving around in such a way that you don't notice/hear the phone going off. I've missed calls that way. But I guess I'm not in that situation enough to justify a new device...I mean, that's helpful, but we're not yet that far removed from a time when we had to arrange our rendezvous and appointments with no expectation that we could contact people in mid-transit (i.e. before cell phones).
I don't consider myself a huge Luddite. I waited in line for the first iPad, but with that, I felt the value proposition was obvious: this is a computer you can walk around with in one hand and read/navigate/etc....even just reading from a tablet is obviously appealing, in the way that reading a physical book/magazine/newspaper is more appealing (despite limitations) than from a laptop or desktop. The value of iPods and iPhones was never hard to figure out either, even if you doubted whether or not they were worth the price over their competitors.
I wish more folks took your perspective on notifications. We need to reduce distractions, not make distractions less distracting. Of course for many companies like Facebook this leads to slower growth and less engagement, so I don't see it happening anytime soon—that is unless we all take your perspective with respect to technology and change the default settings to notify us of only important/time sensitive information.
I think in practice some of your guesses about notifications and interruption are proving wrong for most people because of the phenomenology of the Taptic engine.