It doesn't matter what settings, PC, mouse or whatever some people use they will never improve. It's not that they don't want, it's because they can't and eye–hand coordination plays a big role in that + reflexes.
Some people just don't have it in them when it comes to FPS games. I knew people in q3 who played for years and never improved.
Also, it's pretty easy to get used to low sensitivity, in the beginning it might look slow and hard to move around but with time you naturally adjust to it. Same with FOV, you don't have to lower your sens to make the game a bit slower, a lower FOV will result in slower sensitivity too. In the end it's all in your head.
But it's true that with higher sensitivity it's easier to strafe jump and do circle jumps. But it shouldn't be a problem for people who already know how to strafe jump.