Do what Roger Cicala suggests - send the repair center your test images, with methods and with commentary on your specific issue.
They ignore them. Well that is my experience, I used to send prints and CD's with test images on along with the lens for repair, you get them back unopened.
The lenses are put on test equipment and are either up to factory specs or not; if they are then you get it back, if they are not then they work to make it so.
De-centering is a correctable alignment issue, I wouldn't think field curvature is as it is an inherent characteristic of any design.
Many lenses produce horrible comma in star images, but are superb photography lenses none the less. A star field test is not a good test for lens, unless your main subject will be star fields. Comma is but one aberration, and is often accepted in mitigation for reducing others.
Personally I think they are all within a hairs breadth of each other, comma will show much worse with a darker sky so your rental comparison is not a fair one. Similarly, the stars are much smaller with the 17 so produce less comma too. If you are not happy with the lens send it back, but if it is in specs they will just return it again. I'd do better IQ tests on more common subjects. If the lenses primary use is star fields I'd look at getting a lens more suited to the task, but wides and ultrawides are always going to be a problem.
A vastly cheaper alternative is to use the 1.4TC MkIII on the 17. One stop of light less, but excellent IQ and using the center of the lenses image circle.