Why do I suck at this game

I love this game. I dig nearly everything about it. The setting. The map. The pacing. The gameplay. The gunplay I just can't seem to do well. The enemy seems to strafe unbelievable fast as i attempt to shoot them and I feel like a sitting duck. I know I can get better with the abilities and movement but I feel like I'm not much worse than anybody else I'm seeing. I just can't fucking hit shots in succession to finish people off. Am I that bad at aiming or am I that bad at gauging gunfights and relocating etc. I feel like people get me in 1 magazine a lot but I can't seem to do the same.

Any tips appreciated.