I had an iPad Pro and a Surface Pro.
Apple has gotten a lot of things right when it comes with tablets; iOS as a whole is designed for touchscreen use. As a whole all their tablet apps are optimized for the iPad. That is something that cannot be beat easily. At the same time because everything is written for the iPad, we don't actually have the same powerful desktop applications some of us want. The latter is where the Surface Pro shines; you have a very capable portable that runs all the traditional applications.
A lot of it is about user experience. In reviews, people spend very little time with these computers, the overall experience might seem better on the iPad. Over time of 2-3 years of using both an iPad Pro and a Surface Pro, the Surface Pro is way more useful and a lot more powerful. Yes I wish the touchscreen implementations very improved on all the apps, but you can't expect every developer to update their traditional applications to support a touchscreen.
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A lot of traditional applications require a precision pointing device, and your finger is a very crude one. That's why all the iOS applications have big buttons, toggles, boxes, etc. You don't see a lot of nested menus that traditional applications have. Although there are a numerous tablet applications for Windows now, the majority of productivity applications require a mouse or some kind. Without the trackpad it would be quite difficult to use these applications.