Now that I have one, I can't disagree with this. My SP4 is the best ultrabook and sometimes tablet I've ever owned.
As a tablet, well...it works in a pinch, but I'd say the iPad is a better all around pure tablet. I do love the pen functionality, and it's actually not half bad reading with it in bed at night (a little oblong, but not terrible at all). But most of my time with it thus far has been spent using the keyboard and trackpad.
I love the thing. Think it's one of my best tech purchases in a good, long while. But when I go to upgrade three or so years from now, I might find myself leaning more towards the Surface Book.