Well your desktop build is horribly inefficient in terms of FPS per $. You’re wasting a ton of money on components that aren’t going to affect anything. If you are actually serious about game design with UE4 then there’s not much of a reason to get a laptop. That GTX 870M is slower than a 660 Ti. 660 Ti’s don’t max out many modern games.
Laptops can’t be upgraded. The hardware in them is obsolete very quickly and then you have to shell out another $2,000 for something equivalent to a $1,000 desktop.
Screens are a consideration as well. I honestly wouldn’t be content with just a single 17 inch screen.