The Surface is a laptop crammed into a tablet shell.
An iPad Pro is a tablet.
So the Surface has more RAM to work on serious projects, more CPU to do them with, and... a far greater hunger for power because of that. Like, 3h of continual use is a pretty good day.
It's also got an OS that is trying really hard to work as both a tablet OS and a desktop OS. Windows 10 is not quite there yet IMHO but it comes pretty close; another year or two of development and it'll be there.
For artists, "runs the Adobe suite" is something of a killer app, and has been since version 1. For other people? Well, what's that one app you really need a desktop/laptop to run? Maybe one with a limited version for tablets, maybe not. You can kick back on the couch with it now. I see a lot of people on /r/surface talking about how they use it for all their note-taking; it's got surprisingly good handwriting recognition, and is, again, ultra-super-portable.
(I hear it also does surprisingly well with games; plug it into your big screen's HDMI input with the casualness of bringing a tablet into the living room, instead of setting up a big noisy Gaming PC, and have fun. I never tried that during my time with it so I can't speak to how well it actually does. I literally did not install anything on mine besides Adobe Illustrator, Evernote, and a few programs for remapping keys/putting hotkeys on the screen.)
It's a pretty serious step into the world where you have one device that works as both a tablet you can poke at with your fingers, and a Serious Productivity Device that runs whatever twenty-year-old monster app that you've been using so long you don't even have to think about half its keyboard shortcuts.
It's not fully-baked yet, Win10 is a mess that still drops you into horrible little control panels from 1995 now and then, some crucial UI elements vanish if you use apps designed for tablet usage in "tablet mode", but it really felt like something magical in the same way my first iPad did.