Again: WATCHMEN and KILLING JOKE look exactly the same. It doesn't matter in which order they were published. They still look exactly the same, with the identical bland 9-panel page-grid, that manifests they strictly followed a script and gave relatively little input to the script as an artist. (as compared to the many other examples I gave of Don Simpson, Michael T. Gilbert, Alan Davis, Gary Leach, and David Lloyd on other Alan Moore stories, where the artist contributed noticeably to the project).

Another that follows the same 9-panel-per page Alan Moore script:
SUPERMAN ANNUAL 11 (1985) by Moore and Gibbons.
Same thing.

I frankly think Moore is being generous to Dave Gibbons, in giving Gibbons credit for what story ideas he offered, and including Gibbons in the process. But I think any other artist would have contributed similarly.
Gibbons' art is unspectacular and functional, WATCHMEN was still an Alan Moore show all the way.