The stats don't necessarily reset, volt and I have been looking at them and for some reason there is a glitch with the "first seen" and "last seen" for players.
It seems occasionally the first seen and last seen become the same and when they do that player won't show up on any of the "top" lists.
You can still manually search for people like K-otic and ryanw who for some reason aren't on the list when they should be. (I was off it for a long time too) Their effeciencies will still be the same. I've been playing since what, about the 16th? and I haven't seen a single stat reset yet. So thats still at least 2 weeks. I think it's just people are getting hit with this glitch. Probably something to look into actually.
Also, I purposely got on and camped to try and get first on my laptop just for the chuckles and pretty much failed since freak and some of the better 1.2 players also got on lol. For some reason K-otic, Expowerranger, and ryanw wont show up though, so I should be in 4th. But it threw me in first anyway. Heh.
I think your only valid point is level of competition and that only has so much of an impact over time. I think knowing when and when not to be aggressive effects how good a player actually is. If you're just dying you're inhibiting your team. At the same point, if you're solely camping you are also inhibiting your team. If you look at my stats on my desktop(the one that's at 5th now) you can see I have a lot of structure kills and one of the higher destruction effeciensies. So I can't be camping all that bad. I'll say that it may not show personal skill level the greatest, in some aspects it does show a lot about over all skill. Because someone may be able to dodge and shoot better than someone else, but if they play stupid, all in all they are a worse player. Take example Amp. He was one of the best maras in this game, but never got any respect for his skill because he just raged and did terribly stupid things up to constant rage quitting. That led him to almost always lose public games and made him useless in scrims. So while amp always outplayed me individual skill wise. I won the majority of 1v1's he demanded on ms server and I almost always showed him up in public games and scrims.
Also, I'm not trying to defend that I'm a great player or anything, I humbly admit that I am lucky if I could be considered in the top #20 of active 1.2 players. I just am trying to imply that the stats deserve more credit than you give them. Other than, I think there should be a longer limit of when they're acceptable. I think 5000+ score, would be more fair, rather than 5 games(I think is the current settings) Because yeah someone can camp 20 kills in 1 game with no deaths and then spectate or build a few games, and they have 20+ effeciency. The stats are more accurate over a length of time, for obvious reasons, because it generally means you've had a variation of skill of competition and you've been pushed into many different situations with many different team variations.