Not going to argue that Windows doesn't boot really fast. It's one of the recent Windows features I've massively appreciative of. However, comparing boot-to-login between an iPad and a Surface seems a little odd to me, since after login Windows will still be loading stuff (depending on what your startup software list looks like) while the iPad is ready to go as soon as the login is presented (assuming there's a passcode set up).
So you should probably be comparing boot-to-loaded-desktop against what's happening on the iPad. Let's assume we're logging straight into the default user on the Windows machine and there's no passcode on the iPad.
The PC probably still wins that, as long as there aren't a ton of startup programs involved, but it's going to be closer.