VAC (the valve anticheat) is not kernel-level. The community alternative is. The official matchmaking is pretty full of cheaters.
I have over 10,000 hours in the game, majority played on official servers with quite a low % of matches impacted by cheaters. The match quality does deteriorate with Premier rating. I noticed a decent jump in cheaters after about 25k rating, although the number is not as much as people like to make it out to be.