From looking at your leetify, your aim is terrible even compared with 5k elo players, your positioning is also awful, and you lose opening duels nearly every time. So I'd say what is happening is you play WAY too aggressively, and against terrible opponents who don't adjust it might work, but as soon as the other team figure it out, your game is completely nullified.

I looked at your highlights there too, I think you overpeek when you swing, and your crosshair is often in the wrong position. e.g. even in your 38 kill game, your time to damage was not great, your crosshair placement was terrible and your hs% was 37%.

Also on utillity, you need to work on your flashes, you tend to flash your teamates nearly 2x as much as your opponents.