I don't hook up any peripherals at all. So I am dongle free. If I want to see anything on a bigger screenI just cast to the TV. USB-C is the way to go. Change is sometimes a pain in the rear and expensive. Even if the Surface devices went all in on USB-C it wouldn't bother me at all. I may be an exception on here. In a year or two most everything will be USB-C. My frustration would more than likely come from Windows 10 and my lack of experience with the OS.
I do some writing so, the keyboard is what I look at. The Surface Book has a keyboard that feels very nice. Surface Pro 4 keyboard even felt good. Plus the Pen oh, that pen. The pen is what would sway me towards Surface. To be able to write on the screen and that gets converted to text is what I am looking at. Can do that on an iPad but, that is an additional device. So economically I could combine all my needs in a Surface product. James, I am not sure if I answered your question or talked myself into a Surface Pro or Book.