That debate is old. lol I just used for general traffic "range". Everyone already knows about its inaccuracies but how many people on here pay for comsore reports? Anyway feel free to debate that or this reply haha.
It ranks the sites traffic among other things... and from my experience it's pretty accurate as well. I have been monitoring alexa data with actual server data for the past couple of years and it's very accurate from my testing.
I see, now that I've read the OP's post more carefully, it does seem they are incorporating "activity" into the definition of "largeness", in which case factoring in Alexa rankings would make more sense.