I'm not sure I really think they are relevant to each other, the surface book is a laptop and more comparable to the macbook pro than the iPad Pro. Now if you can argue the surface pro 4 against the iPad Pro, they are closer.
So what's the more smarter decision to buy?
Macbook pro ($1299) + iPad Pro ($799) + pencil ($99) + ipad keyboard ($169) = $2366
or the Surface Book for $1499