Never met a good player piloting a light 'Mech, have you? It's possible and even probable that a good player conning a light can rip a heavy apart easily. Seen it happen, did it once or twice.
I admit I haven't played since college, but I don't recall being light weight giving any statistical advantage and a whole bunch of disadvantages (less armor, less/lighter weapons, less damage capacity, etc.). What could lights do that heavies couldn't do better? I'm geniuinely curious here.