Hello! Recently, I began to notice a large number of players with low levels between 11 and 80. What is strange? The strange thing is that they play suspiciously well. Are these cheaters? I watched some replays with their participation and can not understand. For some reason, in the end, they occupy the top ranks of the rating, often with a rather high k\d rate. Too high for a beginner. Maybe these are bots (unlikely) or new accounts of old players (higher probability, but why?)?

Most times it's very easy to tell if some low lvl players is cheating. If you watch them they tend to have no game and map knowledge but for example, somehow know that there are enemies in that building, so they try to reach them but they don't know how.
But for what you mentioned, I don't think its cheating. (for what i have seen) Most times new players do very well is when there´s a wave of new players coming into the game (steam sale) so the matches are filled with same skill level and likely same behaviour (from other shooters). so if someones good at other shooters he will have no problem to set himself apart from the others. because they will not yet behave "the insurgency way", they´ll move left-right while shooting, but this does not work like in other games, it would be better if the would land one clean shot instead of killing their accuracy and still get dropped with one or two bullets, run in the open, stand at the window frame, sprinting around corners and so on... (stuff that works in other shooters but gets you killed in insurgency)
then there are the once (around lvl 80) who know the basics and some things so they´ll have an advantage in these lobbies and so they do well.
Or they´re just gods and perform that way

There's definitely a wall hack of some sort available out there (assuming it hasn't been countered already). I reported a cheater for the first time ever last week and he was one of those low level prodigy like you said. At first glance it wasn't super obvious, but watching the replay, you could tell he had a wall hack just by the way he would turn corners and aim in the wrong direction (for that specific corner), directly lined up with an enemy behind walls or even entire buildings. He had no idea where he was going and was clearly paying more attention to the wall hack on his screen rather that what was actually happening in front of him.

That said, I don't thinks it's super common and good players will generally pick up new games very faster. Still, those low level cheaters can be hard to spot as lack of game knowledge is often enough to bring them down to a level that's not immediately suspicious.