Crouching like aimpunch is not lag compensated for. On your screen, you might see someone standing, and shoot him while standing, but once this "+attack" command of yours reaches the server and the server in turn rolls back time calculatively to reproduce the gamestate you executed this command in, the standing player you were shooting in the head might already have crouched. If this is the case, the server will simply assume the player was already crouching on your side of things as well, making your shot miss. Especially the instant nature of crouching in this game makes this a rather game-breaking issue in online play, where crouch-spamming players are impossible to register on precisely.

so will i be better if i crouch spam?

You need to replenish your armor when it drops exactly below 47. That is when full body armor stops working to cover the whole body. Otherwise you should update your armor roughly every time you are at 50-60.

If you already have a helmet make sure to only buy kevlar for 650$ and not the full 1000$ because you will keep your helmet anyways.