I don't have anything insightful/new to say about the vision related stuff, but I'll give my thoughts on stroke straightness, which is directly linked to the improvement process OP talks about in the sense of how much you can learn to trust your vision/aim:
One important aspect of this whole topic is the mechanical part of what it means to shoot straight efficiently. The way I developed my straight stroke was by realizing that for a given stance, there is always some path that the shooting arm naturally wants to go to, if moved in it's simplest possible path forward, rest of the body staying still. The goal is to build the stance such that this path is always straight forward relative to what you are seeing.
There are numerous issues that can stop this from happening, most commonly your body being in the way of the stroke, or some part of your body causing the angle to be off or steer at some point. It's not just elbow/shoulder related, almost every part of your body can ruin things in unexpected ways. Especially once you also consider balance, stability, comfort and ease of repeatability, which are all important principles when building your stance.
Once you find something that works well for normal shots, then you probably need variations for various elevated shots, jump shots etc. it really isn't easy, and there are no shortcuts. Paying extreme attention to your stance, to form a perfectly repeatable, straight and effortless stroke direction, is in my opinion, one of the most powerful improvements that many players never make.
This process is tricky, and greatly benefits from outside perspective, ideally a coach or a better player than you giving you guidelines, alternatively online resources/books/video feedback if coaching isn't an option.
It is so easy and common to half-ass this aspect of the game during your development, form a stroke that goes somewhat straight and get a false sense of mechanical perfection from easier shots going in consistently. Then perhaps blaming aiming, lack of experience or lack of talent for the harder shots not going in most of the time, when the true culprit is most likely the consistency/straightness of the stroke not being pushed to the next level.
The less consistent your stroke, the less trust you can build in your vision/aim. The straightness of your stroke is directly linked to the ceiling of your skill level.