You picked a horrible example. Rolex Sea Dweller is amongst the thickest of dive watches because it's designed to be taken to extreme depths (depths no human will ever descend to in a diving suit).

Here's Piaget Altiplano for example: http://blog.luxurybazaar.com/wp-content/uploads/2014/02/Piag...

or

Blancpain Billeret https://s-media-cache-ak0.pinimg.com/236x/62/39/fa/6239fae47...

Well, that’s true, but you went to the other extreme of the spectrum: Piaget’s specialty are ultra thin watches, I don’t think it’s a much better example.

Mechanical watches under 7mm are already considered thin; more usually they are 9-11mm. Quartz are easily thinner.

I think smartwatches currently around look thicker because of case and lugs design. For example, the Sea-Dweller is 18mm, but the side of the case is not flat all the way like the 360, the case back is actually inset, so it’s less noticeable.

I'm not choosing between a Rolex and a smartwatch; I'm choosing between a smartwatch and nothing.

The 360 is visibly larger and taller in the picture, and the strap ending at the bottom doesn't really help.