It doesn't take good aim to hit a stationary deployable. Which means a deployable not only removes the need for the deployer to aim, but robs the enemy of the need to aim as well. Pick a random high aim weapon, if you are poor at it, you're going to take just as long to destroy a turret then if you are good with it. I think a better method is having a weapon that is quite forgiving because that removes the stationary, boring target of a deployable. You are only aiming at the individual, which means you're aiming at moving targets which should get harder to hit over time. This also removes the problem of the turret becoming less effective in organized play because they are less effective because coordinated teams can easily take out deployables together. While a player with a gun that requires less aim is going to be mobile and coordinate with his team, so shouldn't be less effective.

With all this being said, i don't think its a good idea to design FPS in a way where some people don't need to aim. Most people will feel cheated if they die to someone that isn't aiming. If i am landing my shots better then someone else, i expect to win the engagement. Also, at higher levels no one wants to play the role that requires no aim, not because its weak, but because its boring, they play FPS to aim, its the defining skill of the genre. In TF2 the medic is the strongest class in competitive, but you had the best NA medic move down to intermediate to play scout instead, because medic is boring because it required little aim. Designing it so someone doesn't benefit from good aim in FPS is like designing it so someone doesn't benefit from high APM in starcraft.

It is better in my opinion to just have weapons that utilize different types of aiming. You need different skills to land an airshot with a solider, to be effective with stickbombs as a demo, to land meatshots with a scout in tf2.