I have written my own Gcode before and from my experience I would think it would be very difficult to make code that would out-perform a slicing program. The slicer is an advanced tool that has all kinds of algorithms and coding that optimize tool paths and g-codes. little things like the way cura "wipes" the excess plastic off or can be set to compensate for thinner lines by accelerating etc. Also it knows all the code and is pretty much an expert at it and i would think it would take many many years just to learn the code and intricacies of the codes and what they all can actually do.

I could be wrong but linear and circular interpolation is just a small part of g-code so i would think the big difference is all the rest of the details.