Long Straight In Draw Shot

I haven't read all the posts.
But I did read that you think your mechanics are off.
That's the first thing to fix.
Dead straight shots are tough.
Try this.
Aim through the object ball to a spot in the middle of the pocket and just stroke it.
This way you take the aim on the object ball out of the shot.
I would try just shooting the cue ball alone into the middle of a pocket and when that gets real comfortable stick a ball in between the cue ball and pocket.
Worth a try.

I'm not a instructor but I have been working on my alignment and stroke. The long straight draw shot is the toughest. I set up 2 hole reinforcements straight to a corner pocket. I had my wife video me and watch me so I could see my alignment before the shot and get my shoulder, elbow, and hand all on the same vertical plane. This straightened out the loop in my stroke. Now every practice session I start with this drill and when I am aligned right my tip is straight down the line after the shot. and the cue ball comes back to my tip.