500 kills or 8000 is not INSANE for an aimbotter/hacker. They do not actively go every single day hunting through reports looking for hackers. Remember right now there is no REAL system in place that auto-detects (which they've replied on reddit they are implementing) *This is a huge step forward* they are working on the algorithm for it though to make sure innocent good players dont get banned from it.
Now for the kills, back to the topic of they can't search reports everyday. Remember that A LOT of people report people that kill them without even spectating just because of rage and people have to comb through these reports to find the ACTUAL hackers and this is extremely time consuming so many people get past the radar. We can blame both sides for this because people just spam that button without making sure half the time and we can blame the lack luster anti cheat both sides have a fault here.
Now for a legit person 500 kills seems pretty decent but for a hacker they are pulling 10-20 kills a match most times never under that and can finish matches in 7-10 minutes because they can SEE everyone and almost insta drop them. Which means within an hour they can pull 60 kills already if they ONLY pull 10 per match. So within one full day of let's just say for simplest math here they run the game for 10 hours that's 600 kills in ONE DAY this is a MINIMUM.
Any game most hackers will often be able to bypass or get around being banned for longer than just a week so they can easily reach those kill counts without much issue. A legit person obviously would take weeks/months depending on skill level to reach those numbers but for a hacker 7 days is more than enough. So remember when you see those 1000's of kills on a hacker that they don't necessarily have to be old accounts could be just a week old.
Also remember it's possible that someone played LEGIT for a long time and decided they got bored with the game and said screw it let's just troll everyone and then downloaded the hacks considering they are pretty available. So that kill count could have also been legit to a certain extent. Also no aim bot has 100% headshot simply because auto-aim does not account for bullet drop which is why when you spectate a hacker you'll see they miss a LOT more shots from further away and hit every single shot at medium to close range.
