My Surface has a faint bright band along the left edge, it's has a yellow tint to it. I don't believe this is a defect. I think this is a normal characteristic of LCD displays and how they distribute, bend and reflect light. I'm not saying it shouldn't bother you, just that I would bet every single LCD of this type will show this. Unless it's particularly bad on your device, don't expect a replacement to be better unless it has a different design of LCD.
I don't think the way the Surface is assembled has anything to do with this. I have noticed this same warm glow along the edge of different LCDs in all types of devices held together both mechanically and with adhesive tape. Right now on my desk I have a Dell U2412 monitor and a Nokia 1520 phone. Both also show uneven lighting on at least one edge with a white or light grey background. This is definitely a different problem then the distinct yellow patches that showed up on earlier Surfaces in areas where the LCD overheated. That would come and go with temperature and could get worse over time if the LCD was permanently damaged.
As for the light bleed at the top corner, I don't think that is normal for the Surface 3. I checked several demo units and the one I bought. None had noticeable light bleed. Mine is about as good as it gets for a large IPS display. The light bleed in the photo here is terrible. I could not live with that. One thing you might want to check is if the body of your unit has been bent. I noticed mine had a slight curve to it. I could straighten it with firm pressure from my fingers. I think the magnesium body is soft and thin enough it can get bent rather easily and it will hold the shape rather than spring back like other materials would. If there was any twisting of the LCD frame that could definitely cause light bleed.