With the risk of producing a litle anger in you(not intentional) I think you shoud think a litle more as im not seeing lots of logic here.First if you are serious about doing game design as a hobby>avoid intel gpus.There is a reason they are on the bottom of the food chain.(for me,doesnt even qualify as such).
A R9 M390 is a ¨¨all most¨¨ medium level entry laptop gpu.(will even perform 20-30% weak under osx than windows)(there is a reason bootcamp exist,because someone at apple isnt doing his job right with the optimization).
You see imacs with insane screen res,but the question is, can the provided gpus they have will work at good framerate at 4k?
The answer is no.Atleast ue4 wont.Games too.You will have to lower the res to 1080p and hope to get 40-50fps at best.
You are not telling us the specs of that windows laptop.
I woudnt call windows ****** as most of the software out there is developed for windows and not mac and since companyes use it, than is profitable.With time you will want to make money,than money and feel good doing it.
If you want to go pro,dedicate your time to this and finally make a living out of it,you will invest your cash carefully.If its just for fun/hobby,than go with the mac and a amd gpu.