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.
Move quickly, and you get more bang for your C bills. My friends and I played on a credit system, and having three smaller mechs made for some nice gangbangs.
Oh yea, if I'm running circles around you, and knocking your to hit up to levels beyond god, well, your P cannon's just gonna be a big, nice toy. Yea, my to hit's horrid too, but I invested in small, light weaponry, going for the million papercut ideas....
I'd throw in a tag or two, and like I said, let off with some stupidly powerful artillery piece (usually an equipped heavy, guarded by more light mechs in case of attack...) and pound away...