I know a lot more than you do.
I have made a few cheats and made a few videos on youtube showing how they work, when I was in the supposedly anti cheat team for the main IG pug group, until I realised only players that are not popular get banned when cheating and others are allowed to get away with it because they are friends with the right people.
The kills only feel instantaneous to you because on your client because of what you are seeing in game, that person will see something slightly different, the server will see things slightly differently to both of you. What you see is not what the enemy player sees and vise versa.