I can't believe I am going to say this here. I must be insane....
I met a guy the other day that had a Surface Pro and loved it. He'd gotten rid of his iPad for it. He preferred it because he was convinced served his purposes better than the iPad. He used it to take pictures and then notate those pictures, which is surely something he could do as well or better on the iPad. Still, he claimed the Surface offered more precision and worked better for the task than the iPad. Is that true or was he simply unable to find the right app on the iPad? I think he probably just didn't find the right app, but he is now convinced the Surface meets his needs better than the iPad.
I have no doubt, that for a small percentage of people, most of which would be in professional settings with specific needs, the Surface may very well suit their needs better than an iPad. Especially with the pressure sensitive screen, as the guy needed to annotate as you state. For him the Surface may be a better suited tool.
The point is that for MOST people, the iPad will suit their needs in a more intuitive way, and is a better overall device. From size, weight, battery life, stability, responsiveness, intuitiveness, ecosystem, etc etc.