I bought a 2003 EC125 for my son eight yrs ago with the specific purpose to be lighter than the larger 200, 250 and 300 bikes. We built the 125 with smaller lighter tires and tubes. The end weight was 220lbs with 1/2 tank of fuel, bark busters and head light. Our EC250 and DE300 GG weighed around 240 to 245lbs. My XC327 with hand guards, lights, Dirtstar rims, skid plate and pipe guard, big tires, HD tubes, big gas tank and full of fuel weighed 250lbs The GG 125 bikes do feel considerably lighter than the larger engine GG bikes.
Most of the 125 frame is the same but they are different where the engine mounts. The GG125 engine is much smaller than the bigger 200, 250 and 300. I do believe the 125 frame is a bit lighter because they used less metal around the engine cradle area.
Avoid the GG MC125 unless you want a race 125 which is miserable for trail riding. While the US MC250 was pretty similar to the US EC250 engine the EC125 and MC125 engines were considerably different in power delivery. I spent years trying to make a MC125 act more like a EC125 for my niece. Ultimately I built her a 144cc engine out of the MC125 and that has some nice manners.