I do hope I didn't give an impression that I was doubting that camera or lens error, or that a combination of the two were perhaps to blame. I do accept that certain styles and genres of photography give rise to a possible focus problem being far more identifiable especially in portrait, or other closer work, where an errant focus would be more noticeable. I include street and architecture in this scenario too.
My work is largely wildlife and landscape. With wildlife the only time I use AF-C is when I am using dynamic 51 point or less and 3D focus mode for birds in flight. I am indeed fortunate that the instances where the target has selected left or right focus points, the capture has been in focus. With landscapes I only use Centre focus in AF-S, so there is luckily no issue for me.
No one has really persuaded me zoom lens errors can be coped with by any angled tests unless either a permanent focal length is used, or perhaps a decided average of staged tests across the full focal length will make an overall improvement.
Perhaps I am posting in the wrong forum, but I do value others opinions and ideas on the fine tuning issues.